Of course you increase speed with an increase in drawlngth. But it's a poor way to get speed. You should optimize your drawlength to conform with your shooting form and never compromise it. It's a lot easier to gain speed in other ways.

You can shoot a lighter shaft. And by that I don't mean cutting them a little shorter. Cutting 1 1/2" more off will only amount to about 2-3 fps. It might be worth it though in your case because you are realy pushing the envelope for spine anyway. You can compliment this with a lighter point--say 85 grain.

What all do you have on your string? Clean off all you can. Move string silencers as close to the cams as you can. Reduce the length of your center serving to about 3" long.

And while you're at it buy a good set of aftermarket strings made from BCY 8125 (winner's Choice, Vapor Trail, etc). I gained 11 fps just changing from the factory strings last year.

There is only so much you can do, but increasing the drawlength is never the best option. Frankly, the best option, if you want speed, is to spend the money for a real speed bow. Your bow is not a speed bow. It's a good bread and butter hunting bow.