I'm running both, or was, a 2011 Revelation and a Coil U-Turn, 150mm Sektor. They're both good forks, personally I like the way air forks ramp up, but that's a personal thing, both quite plush and good over small stuff. The big difference is the high speed rebound damping, current Revs and last year's Team versions have a separate high speed rebound damping circuit a bit like the Push mod to RS forks.
Mostly you won't notice, but if you really hammer through, say, rocky stuff at speed - think Potato Alley in the Peak for example - the standard RS rebound damper eventually can't flow enough oil and the fork pretty much locks up, or at least gets very 'lively because it can't move fast enough.
With the Dual Flow or the Push upgrade, it doesn't, just keeps on working. Don't know about the spring, I'm about 11 1/2 stone or something, more with a pack, Sektor std spring works fine for me, ditto standard Pike.
I think the Revelation is a better fork - lighter, more tuneable, better high speed rebound, but the Sektor is ace for the dosh and a Sektor Coil U-Turn with a Push Upgrade, if they ever get round to doing one, would be nice, I think. If you don't ride through rocky stuff at speed, you probably wouldn't notice the high speed rebound thing in the same way that some people swear that the Push upgrade made no real difference to the Pike, it does, but only in certain situations - if you're never in that situation, it doesn't really matter.
Depending on how / where / how fast you ride, that may or may not be an issue. In the Peak, on a full susser it is, definitely.
Don't know about the two step thing, don't have one. I've got a 2.5 Minion DHF in a Revelation at the moment, it's not huge for a 2.5, but it's biggish.