That sounds very similar to the setup I'll be getting into in the spring. I agree with losing the 80# limbs, but to each his own.
I wouldn't shoot anything less than 480 grains with that setup. Others will tell you 5 grains/lb are fine, but heavier is usually quieter as the arrow absorbs more energy. I shoot a few different grains and see how they hold. As far as an estimation of speed??? I 'll take my rookie stab in the dark at between 305 and 315. All set up of course.

Trushot }}------>