i don't think it will be that much different to your old one to be honest. you may find spool up is just slightly slower but if your running standard-ish boost
there won't be much difference. you will be better off when you come to chip it though cos the tuning bug is very contageous and no doubt you'll be planning this and that when you get power hungry. at least you'll have one of the main ingredients to run big power ready and waiting. all you'll need is a larger intercooler and you should see about 175bhp or so at about 15 psi with the chip, maybe even more

with the dodgy oil return, definitely do an oil change and probably a good flush out wouldn't hurt. i would possibly have your oil pressure checked as well, might be a dodgy oil pump causing starvation. never really heard of a return causing failure but hey , they are built by ford

anyway good luck with the turbs