My personal reasons:
1. F4is have a well known problem with their CCTs. Honda doesn't always replace these under warranty.
2. The F4i seat is rock hard
3. F4i can't use swingarm spools
4. Single low beam light. ZX-6R lights are much much better. Ride magazine rated the ZX-6R lights as 4th on their Top 5 bikes with bright lights list.
5. F4i could use some more ground clearance
And unless you get a really good deal on the F4i, the ZX-6R will cost less as well.
2000 ZX-6R