You're doing it backwards from how I would do it- I would go to the dyno and try different A/F ratios to see what gives me the best HP.
For me, I ended up at 12.2:1 (NA). If you're a turbo car, I would start at 11.5:1, then try 11:1 and see if that helped or hurt. Then try 12:1 and see if that helped or hurt. And it's possible that you want different ratios- for example you might want 12:1 above 4000 RPM and 11.5:1 below 4000 RPM. The dyno will tell you!
BTW, it's a good idea to have your VE tables nice and accurate before you go, that way you don't have to fuss with tuning VE and A/F at the same time.
(And while you're there, be sure to discard your first run- no matter what, your first run on the dyno will produce more HP than the rest. Do one pull, throw away the results, then use your second pull as your baseline for comparison.)
On n/a motors I like to start at 13:1 in the upper rows. You may wind up finding that a little richer than that will produce the best power, as Bob said, and you may find that leaner works best for you. It varies for everyone. 13:1 should be a good starting point though.
