You could get an extra 15-ish+ Bhp, and 20Nm of torque.
Being a 2.8 litre, it's not giving it's all as it is, but you'll have the M52TU engine (which has double vanos) rather than the earlier M52 single vanos that had the nice easy M50 manifold swap.
You do have the option of fitting an intake manifold from a 330i with a couple of custom bits to link everything together, and then you should see more like 230+ bhp in total.
Fuel economy won't change from it's current "style", ie if you drive it gently, it'll carry on making the same MPGs, maybe a very slight increase if you are lucky.
If you drive it harder all the time and don't have great MPGs, then it might get a little worse.
It's the same as original I guess, choose power or economy when driving, and it'll give you one or the other.
The main bit would be throttle response. It will feel sharper and more eager, which is something you'll always get and that's what you'll mainly be using.
Increases in only the peak power wouldn't be much use if you rarely got enough clear road to stretch it's legs!