stress increases exponentially the higher the rpm you go. 7-8k, big difference. 8-9k...even HUGER difference.
IMO, keep it at 8k, unless its a pure track car......then try 10k and see where it gets you
BTW, Im interested in seeing if you pump all the oil out of the pan, into the heads, with that 12mm pump.....I hope you don't starve your bearings by cavitating if this does happen.