I would also strongly recomend a higher stall speed on your converter. I beleive that the fact that you picked up as much as you did from a 3.90 to a 4.56 gear illustrates the need for a higher stall. .6 in the 1/8th is almost a full second in the 1/4. I could be crazy, but that seems like more than you would usually gain with a setup like yours. I have heard of similar cars going from 4.10 to 3.55 and only loosing around .15 in the 1/4. My guess is that your motor boggs so much off the line, the more gear you run just gets ou past the bogg sooner, so you go faster. If you got a converter that did not bogg, I think you would be fine with the 4.56 gear. All of the things you mentioned have the possibility of getting you more power, but no matter what you do, you need more stall. I would call comp cams, tell them your situation and see what they recommend for a converter. With the cam you have, I bet you could use something in the 3500 range. You may not to change anything else to get what you are after. Also, what do you have for exhaust?
Adam