I have a 632" with 10.5:1 comp, fully ported and polished dart 360 heads, dart tunnel ram, 2X775 race Demons, comp solid roller 280/288 @.050 .785 lift on 115 cernterline. made 900hp @6600 rpm. @5800 it made 840hp. I very seriously doubt you will get the 850hp you are looking for with less compression and a hydralic cam. I've had lifter issues in my motor and thought about going to hydralic rollers, all the manufacturers and builders I spoke with thought I would give up 100hp. I didn't want to loose that much so I have a set of Schubeck radius lifters going in today. Oh, and I run 93 Octane with 32 degrees of timing. I would say 775-800hp is more likely. I spoke recently with a 25 Daytona owner from SC woth a 622" motor (same heads, 10:1)solid roller and a dart single plane manifold with a 1250 Dominator that makes 840hp at 6300. They just arn't going to get there with a hydralic cam. Also the guy who built my motor knows how to make big power he primarily builds drag motors and has built several 500" NHRA pro stock motors.