The Irvine is more trouble than it's worth, IMHO. AJ uses them, but they are re-worked. The stock ones I've seen have not impressed me. And Sig is the importer, which is enough to convince me to have nothing to do with them.

The OS FX is the best all around combat engine IMHO.

I mostly run the Mag .28 myself. On a mousse can, they are as good as anything out there, and dirt cheap. Yes, Lee's are reworked, but mine are totallly stock, and I certainly didn't lack for power this year. But the carbs require TLC. I've been using them for 2 seasons, so I'm good at keeping the carbs together (usually).