don't take this the wrong way.. .but $ invested into engine/performance might not give you a good ROI because the F4i will be underpowered by modern 600s, i.e. r6, 600rr, gsx-r, kawi. unless it really is just for you.
that doesn't mean you can't go fast and have low(er) laptimes, but you'll get frustrated by others who'll pass you on the straight and putt it around the corner (the likes of me on a 750!).
but you'll learn more braking/corner speed this way. so your investment on seat time, rubber, suspension, brake/brake lines, etc. will be awesome!
"Leaders are like tea; put them in hot water to find out how strong they are." Anonymous