are you talking about trubo lag? aka a delay between putting your foot down and it accelerating?
oil light is pretty much engine shagged light, if the pressure is low enough to turn it on, your engines already done for. that said, if it does go out then it is building pressure. it is 100% worth getting it checked out to see if the oil pump is on the way out.
2.5's are known for being some what unreliable in standard form, so milage is a tad irrelevant im afraid.
Clutch wise if its still on the origional clutch then 70k isn;t bad, mine was pretty much dead at about 62k miles on the car, although i dont know if it was the origional one or not. Is there much travel between initial bite and full engagement?