Regarding the ZXR, one thing to note is the fact they seem to pop head gaskets with alarming accuracy at 20,000kms, and any sign of cam chain rattle. walk away - infact run as its not long for this world.
i had one (L) and it was a nice bike, quite big but a bit rattly and felt a bit weak, but they can be made to go quick and pump out big BHP numbers but be warned they wont do it for long.
similar story for the FZR.
infact, after owning a ZXR, GSXR (Gk76A), CBR NC29, NC35 and NC30's i would plump for the 30 every time
they are not easily tunable, but the handling is good, parts are easily avaialble and they really are tough and will last for years. the 35 handles just that tiny bit better, but it feels smaller and not really worth the extra £1000 IMO
i do love 400's and i bet you wont look back once you get one. good luck