8000rpm isn't too bad, as long as your oil pump is up to it. Look at a brand new 12mm factory pump with extra shims, or even a Cosworth modified OEM pump as a minimum. If you want to spend a bit more, JUN or Cosworth high volume pumps are probably a better choice. Dry sump is the ultimate of course

When you start pushing 8500rpm, it becomes a problem.

The bearings tend to get starved on the side of the journal where there is no oil hole, due to the oil film breaking down because of centrifugal force.

Cross drilling crank is necessary for 8500rpm+, and most people would probably tuftride or nitride the crank to strengthen it after drilling. All this costs money though, and its just another option that you have to weigh up.

Many aftermarket cranks have the cross-drilling as standard.

No one said modifying engines was easy