QB78 - Power Mods - What Next ?

Maybe some of you QB experts can give me some insight.

My Qb has the typical mods

Bolt Probe Drilled to #16 Drill Bit
Barrel Port Drilled to #16
1/4" Poly tube breech seal
Lighter valve spring
2 holes drilled into face of valve housing to improve co2 flow
Washer inside valve has got the 4 notches, so it kind of looks like an Iron Cross.

So far with these mods the rifle is shooting 700-705fps with a 14.3grain Pellet.. It is still being used with powerlets, I don't like the look of a tank hanging off the front of a rifle so I havent gone to a big bottle..

What else can I do to increase the velocity even more? It's used only for hunting so shot count isn't too high on the priority list.

Thanks in Advance