They know each other inside-out as a result of having squared up so often in the past. As well as having gone head to head on such a regular basis, most of the protagonists are Irish training camp regulars. In addition, many of them have been Test match colleagues.
Given those circumstances it is improbable that either will be able to catch the other out. So with the element of surprise removed from the equation it is going to boil down to who plays the better chess on the day.
At this level, securing set-piece possession on their own put-in/throw-in ought to be a given. That being the case it then hinges on who wins the battle at the breakdown, produces more go-forward ball, outdoes his opposite number in the personal match-ups, maintains discipline, bags chances and plays with greater intensity for the full 80 minutes.
So let's examine the various components: front five forwards, back rows, halves, midfield, back three, the benches and the coaches.
If both are at full strength the front row showdown will see Ulster's Tom Court, Rory Best and John Afoa packing down against Leinster's Cian Healy, Richardt Strauss or Sean Cronin and Mike Ross. Bar former All Black and 2011 World Cup winner, Afoa, each of the others is an Ireland international.
Move back one division and it's Johann Muller and Dan Tuohy versus Leo Cullen and Devin Toner or South African Quinn Roux, the only uncapped player of the five. Opposing captains Muller and Cullen are vastly experienced big-match performers.
There is little to choose between those two units, though last time out against Leinster the Ulster scrum was particularly good – and that was on a night when Afoa was absent.
ROBBIE Diack has had a tremendous season, winning the Belfast Telegraph Most Improved Player Award and a place in Ireland's Development Squad. And when Iain Henderson has lined out at blindside, he has excelled, too, witness a Heineken Cup tackle count of 62 out of 66.
At seven, Chris Henry's solitary miss in 78 attempted tackles this season's Heineken Cup made him that tournament's most dependable hitman.
Nick Williams? PRO12 Player of the Season and IRUP's Player of the Year. Enough said.
But Leinster have a pair of Lions in Jamie Heaslip and hopefully-fit Sean O'Brien, with Ireland-capped duo Shane Jennings and Rhys Ruddock, plus promising Jordi Murphy, all vying for inclusion.
The winners of this battle win the war for their side.
ULSTER have superiority at nine, Leinster hold the ace card at 10.
Ruan Pienaar is one of the best – if not the best – scrum-halves in the world. Blessed with a full repertoire of the skills required for this pivotal role, he can pass off either hand, box kick better than anybody in the game, thereby keeping his team going forward and the opposition guessing, break or create something from nothing.
Ask Andrew Trimble who availed of Pienaar's sublime back-hand pass to score that try against Connacht.
Isaac Boss is not in the same class. Paddy Jackson is learning a lot, very quickly, but Leinster will target him. And Jonny Sexton – making his final appearance before joining Racing Metro – is lethal.
IN Leinster's case it boils down to who is available. Back spasm or nay, I would wager my house on Brian O'Driscoll wearing 13 before jetting off with the Lions once more. But who will partner him? Ian Madigan looks the best bet to get the nod to don number 12.
The Stuart Olding success story appears to have a fresh chapter added on an almost daily basis with this week's salient facts being a call-up to Ireland's senior squad followed by a PRO12 final outing at inside-centre. Not bad for a boy not quite two years out of school.
Darren Cave has spent his entire career in O'Driscoll's shadow. What a great stage on which to try to match the master.
TOMMY Bowe is PRO12's most prolific try-scorer of all time, Andrew Trimble has notched up a personal best one dozen touch-downs this campaign and Jared Payne's all-round form in 2012/13 has been quite outstanding. Bowe and Trimble are Irish internationals; 15 months hence, New Zealander Payne will be.
Leinster have Rob Kearney – ERC Player of the Year in 2012 and, like Bowe, a Lion in 2009 who has been retained for the trip to Australia – Isa Nacewa for whom this is his final match in what has been a quite brilliant career in the Dubliners' blue, plus AN Other with Fergus McFadden, Andrew Conway and Dave Kearney the candidates.
These are the finishers their colleagues will aim to supply. Who among them wants it more?
While Ulster beat Munster at Thomond Park in the 2012 Heineken Cup quarter-final without deploying a single replacement, that was an exception; the days when rugby was a 15 versus 15-man game are gone. Now it's 23 v 23, with the quality and timing of the substitutions as important as the composition of the starters.
For years we have marvelled at Leinster's strength in depth and the calibre of those they have been able to introduce from the bench.
But now Ulster are able to do that, too, with Mark Anscombe giving ample meaningful game-time to all of his squad, a point he underlined eight weeks ago at the RDS by sending five fresh faces into the heat of the battle. They were not found wanting. Significant.
TWO New Zealanders whose sides finished first and second in the PRO12 table before winning their respective semi-finals en route to this.
Ulster's Mark Anscombe – who sent Leinster's Joe Schmidt a text congratulating him on his appointment as Ireland's head coach – knows that with this being his rival's final game in charge, he will be fired up to leave on a high. The Leinster players, too, will seek to give their much-loved boss an unprecedented Amlin Cup-PRO12 double as a going-away present.
But the man nicknamed Cowboy has spent his first season with Ulster proving that he can shoot down opponents and win with the panache of a cavalry charge. Be warned, Dead Eye Joe – he may send texts but he doesn't take prisoners.