With your non-standard beam end conditions it is probably time to do some simplified FEA if you have that capability. Your 10 foot 4x8 beams weigh 275 lbs each. Making them taller definitely helps (by the cube of the height). But also linearly heavier. Maybe diagonal braces or a middle set of leg stands would be better. Decide what deflection (sag) you can stand and build the lightest structure that gives you that.