Having just bought a 99 spec car a bit confused over what fuel to use 95 octaine or 98

It will run fine on 95, but you will get slightly better performance and smoothness from using the more expensive 98 stuff.

Some owners report better economy from 98 as well. Give both a try, but you'll need to run at least two full tanks of 98 before you'll notice the difference, unless you get the ECU reset by your Subaru dealer (who may deny any knowledge of the procedure!)

It's a personal choice at the end of the day, but I'm quite happy to pay the small amount extra for better running and performance.