Thundercat Yeah!!!
I can't tell you that I've riden the F4i, but.....
I've had a YZF 600 R for three years now, and I love it. Very Very streetable, nimble and quick. I thought that when I bought it, I'd be trading up in a year or so, but just haven't found a good reason to. I ride with some guys on R6's and R1's and the odd 929.... They pull away from me a bit in the straights, but just a bit, and I have no problem climbing right back up their tails in the turns. In fact, given my (average) riding skills, I think I would actually be slower, over all, on one of the other bikes. The engine does not make the same "peak" HP or torque as the F4i, R6,... but it the torque curve is very broad and flat. Very good for the street, and makes gear selection for the corners less critical. Any race tuner will tell you that if you have to choose between peak HP, and more torque across the rev range, take the torque.
Comfort: I've gota ride an hour to get to any twisties, and then an hour home. Not uncommon for me to ride easy 5-6 hours only stopping for fuel and water. And the G/F loves to ride on the back.
I bought the bike used, 1 season and 1300 mi old, and got it for about 60% of the New sticker price. So the comment about resale value is dead on. Don't buy new for only a year or two. You'll take too much of a beating on the price, but used a year or two their a hell of deal. I don't think you'll find a better bang for your hard earned buck.
Issues I've had so far.... NONE!!!! I've changed the oil every couple of thousand miles, tightend a bolt or two, changed the break pads, and just put on a new set of Metzler Sport Techs. The new tyres are F*#&$^% awsome!!!! Like having a whole new bike.
So if you can get passed the cheesy name "Thundercat," I can tell you that you'll love it for a long long time. Just a great all around sport bike.
Ride hard.
Stay safe.
Later
:twofinger