Any idea on what miles you normaly get out of a tank.??

Im running standard map at the moment and get around the 300 mark before it drops below the 1/4 mark...
 
dont no what i get out of a tank put a tenner in last night and reset the trip so will see how many miles i get to a tenner but its really buggin me any more suggestions please
 
going stage 2 in the morning any ideas if this will change anything to do with my fuelling problem .Clutch is slippin nw aswell so am not even gona be able to giv it a thrashing on the way back gutted am fitting vr6/g60 setup on sunday so nt to bad changing clutch and fltwheel after map wont affect it in ane way will it wont have 2 get it mapped agen will i