Re: K5 or K7
I'd say you can't go wrong with either. I own a k5 however, would probably rather a K7 and here's why.
The k5 is very aggressive (not necessarily bad) for a number of reasons, where each on their own would make an aggressive bike, let alone a combination of them being; the k5 has a very broad torque curve, power starts quite low, meaning even if you go WOT at 6k, it will happily lift the front wheel (1st). Also the wheel base feels shorter, even if the numbers don't seem to be, it has no issue stepping out, and quite often is considered high side happy, which I do not disagree with.
The k7 on the other hand, make more of its power up top, and makes more of it, just look at the cam profile. It also comes with what feels like a longer chassis where its happier to step the rear out and leave it there rather than high side. Another plus for the k7 is the computer can be made to have alot more functions than the k5 factory ecm.
weight wise, everyone claims the k5 to be lighter, but truth be told, once you remove the cat and dual exhaust, there isn't much in it if at all.
there a numerous difference, other than whats been mentioned but, how detailed do you want to go? and really anyone of them is way more bike than 'anyone' needs on the street. That being said if its a track bike, it depends on what you want from the bike.
GSXR = The go to thrash bike