The stock pump is what, 12-15 years old by now? I would change it anyway, no guarantee it will take the extra power your asking from it. A new (I stress brandnew) stock GTR pump can handle about 260-280kw max, GTS-t's I would imagine the figure is abit lower.
Don't get a Mine's ECU, they are tuned for 100 RON jap fuel. All Skyline sidemounts heatsoak up badly, I wouldn't put more than 200kw through a R33 one.
It's not a matter of how much power the side mount can handle, it's how much your stock turbo can handle, which is not more than 10psi.
I hope this answers your questions.