I'm going for a Raceland myself - on a mildly standard 16V engine, I doubt you're going to notice a world of difference between the Raceland and Piper. I'm a big fan of Piper stuff as you know, your VTR pulled really well with that manifold on and it was much better quality/ easier to fit than the Supersprint I had.
There's no doubt in my mind that given back to back RR results, the Piper will perform better - I don't think the difference will be worth the extra £160 the Piper commands though. Yes, the Piper will be easier to fit but how often will you be changing manifolds? Plus I think my car could use the extra ground clearance of a 4-2-1... my lower strut brace catches the bottom on my mates rolling brake tester (for MOT).
But hell, if we all followed the crowd our cars would be exactly the same. I don't think you can go wrong with either a Raceland or Piper imo mate. It's your money.