I use the felt washers between the mobo and screw, not the standoffs. Just to be sure you get a snug fit, but not overtightened. I've seen a lot of people say if you use them, the mobo won't be grounded to the case and it causes problems. Well, the whole point is the mobo is grounded to the PSU and not the case, so the PSU can do it's job protecting your components. Aluminum cases don't make good grounds anyway, now do they?
The rig looks like it's going to be sweet. Get those pics and some OC results up soon.