Right now I am running 300 - 330 till the end (miles) But we are talking about 200,000miles on the car. (And driving in between of 4,000 and 6,500 rpm's all the time)
Before I could reach 450 on the tank easy (552 one time).

About the tank, if you go with replacement of it, you gonna get plastick one and it's about 30L size. My friend in Poland tried to do that and he got screwed. He had to go to a dealer and SO the tank.