There is now way anyone could give you a decent answer to your question with no knowledge of your heads, cam timing, carb size, compression, etc..... That said a big small block like that has to have some really good heads to turn a lot of rpm. You're talking big block cubic inch in a small block platform. Heads on these engines will go into choke pretty early compared to a 350ci engine.
With that said, I would hope that it wouldn't peak under 6800 or so. Basically try raising your shift and see what it says on the time slip. Also, I don't know what rpm you are leaving at on the brake, but I have found that many times leaving at too high of an rpm like a SG car will slow you down. My car is quicker leaving at 3800 than it is leaving at 5500. It gets a run at the converter and uses the torque multiplication better in the early part of the run. Hope some of this helps a little.
Curtis