The only thing to bear in mind if you do keep the pump is that you could potentially increase the jets by a large amount over stock. If you're for arguments sake taking in 25% more fuel, you will not get an extra 25% amount of oil, as the stock pump will not go past it's maximum rate...

Premix is the 'safest' way to go. You can oil up according to your preference and know that you have no delivery worries unlike using the pump.
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NSR300R - Why did i ever have a 250...