I'd second the opinion that I'd rather have a new 600 than an old 900, etc. Many improvements, AND you better check your insurance before you commit. Dunno 'zactly how you'll come out, but I'd be willing to bet insurance on a new 600 is gonna be cheaper than it is on a 3-year old 900? YMMV.
Now on to your choices...
love the F4 but from what ive heard its under-powered.
F4 underpowered? Don't worry 'bout buying a 600 based on it's 'power'. You can throw a blanket over all of 'em. Talk of one being underpowered compared to another has newbiespeak written all over it.
I'm not a big fan on the ZX-6R
Why? I narrowed my choices down to the 6R and R6, but found more to like on the 6R (more comfy/more torque lower in the rev range/great intake howl/better all purpose bike). The two things I did like 'bout the R6 are 26,000 mile valve adjustment intervals and the hugger/undertail from the factory. If it was going to be my only bike, it would be 6R all the way. Since I already have a sport-tourer, thought I might go a bit more track-oriented (R6?), but I ended up liking the 6R best anyway.
Before you follow the crowd, mebbe you ought to read the open-class shootout in this month's Motorcyclist (or was that SportRider). The much vaunted R1 could not be hustled around the tight Streets of Willow as fast as the heavy, old, outdated ZX-9R (I'm still laughing at 'the crowd' 'bout that one)! Last year Motorcycle Online tested all the 600's, and I believe the ZX-6R came in last, but at least they noted that at the end of the day, it was the bike everyone wanted to ride home! They also did a comparo of the 6R vs the VFR, and it held it's own in the sport touring category. I likes flexibility in a bike!
So...mebbe you ought to dig a little deeper before just following the crowd? Iff'n bragging rights are important to ya (not that there's anything wrong with that!), when your buddies pick on ya 'bout the 6R being a dog, just point out to 'em that it:
1. Won the '01 AMA 600 SuperSport Championship
2. Won the '01 FIM World 600 SuperSport Championship
3. Was undefeated in the '01 AMA Prostars 600 Drag Bike Championship
4. Was leading the '02 AMA 750 SuperSport Championship until the GSXR 750's got to Road Atlanta (750 HP too much at RA)
5. Won the first 2 races in this year's FIM World 600 SuperSport Championship (think it's leading the series)
6. Was right there with the GSXR 600's at Road Atlanta-dunno where the R6's were
So...just how much of a dog can the 6R really be?
BTW...I was leaning towards the 6R over the R6 anyway, but as icing on the cake, you can deal on Kawasakis pretty easily (got $1000 off on mine). I couldn't get anyone to budge an inch on R6 prices!
You know what they say...R6/R1's are for experienced riders: Kawasakis are for enlightened riders!