no matter what kind of AEG you get, you're always going to need internal upgrades to make it shoot nice.
Keep in mind there are other factors that affect your range and accuracy more than just the FPS. The first thing you'll want to upgrade is the hopup rubber, it's the cheapest upgrade you can do, and the most effective.
SR25s do use V2 mechboxes, however there are two main types, one has a longer cylinder and piston, the other just has a longer air nozzle. Haven't worked on enough to memorize which is which.