A new grind that is close to HP specs should work great. 15+ MPG won't be hard at all. Pistons are an issue. Seems like most are a compromise. Might be worth it in the long term to spend a few hundred extra and get a custom set. If you don't get the CR right, it will be harder on fuel and low on power. By the time you do some milling to make everything work w/ shelf pistons, wouldn't be that much more.