A friend of mine has a BIG (1400+ cfm) Gary Williams dominator and it works good now, but had to send it back a time or two to get it right.

I would NOT buy a used SV1 off ebay or any other site. Buy one that's been built for YOUR combo! There are a lot of variations w/ those carbs. Some people have had a bunch of issues w/ them, especially the earlier models, but a lot love them. If I was gonna buy a brand new carb tomorrow I'd get an SV1. I did try Sledgehammer's SV1 on my hemi and it did slow down a little, but like he said, my Pro Systems 1200 dominator is dialed in on my combo and I wasn't gonna screw w/ his carb much. All I did was make a couple of jet changes. It was about 1/2 a tenth and 1/2 a mph slower, so definitely not bad.