Hey Chaoticbiker,
I was actually at Okemo the past two days, one on a Proteus 170/19, today on an MK. Never rode an FC, but had a Nirvana prior to the Proteus. I really like the constant radius and old school feel of the Proteus. Definitely less tiring and predictable than other boards I have tried.
The MK is small, has a mind of it's own and great for narrow, crowded runs. Exhausting though. I remember the Nirvana being tiring also and I blamed the SCR. I'm still fairly novice in my abilities so I'm just guessing.
Had a Rev for a while. Never liked it. Felt like it owned me.
If you want to go with the Proteus, I think the shop at Okemo has a 175/20 that they are trying to move. I'm back at Okemo tomorrow morning riding with someone if you want to join us.