They are pretty much the same bikes, the ZZR250 is the entry level road bike for Kawasaki up against the Honda CBR RR (don't bother with the single "R")250 FZR 250 from Yamaha, GSXR250 from Suzuki. When I was learning there was 5 of us learning and riding 250's at the same time. I had a CBR250RR and so did one of my mates, another guy had a FZR250 and the two others had a ZXR250 and a ZZR250. The CBR's were easily the fastest with the ZZR250 the slowest but more comfortable by a long way. the ZXR and FZR slotted into the middle being about the same. Most of these bikes will be "Grey" imports, I got warned off them when I got mine but got one anyway. I did not have any issues with parts or anything that people said I would. Looking at the list you will get a 600 but it will be more of an upright ride e.g. a Bandit compared to the 250's as you will not be able to ride any of the hyper 600's e.g. R6/GSRX/ZX6/CBR600 etc. this is probably a good thing as if you got straight onto one of these you will get into trouble. I went from my CBR RR 250 to a Brand new GSXR600 and then onto an R1 and was for me the ideal progression, I had heaps of motorbike experience from starting when I was about 5 and racing super cross and motocross up until recently and I have had several "Off's" on my road bikes so it will happen. So all the best with you decision, my pick's would be either the CBR RR250 or something similar to the Bandit Chooka