I was looking at 400s too Arctine, but they very costly for what they are, parts are a nightmare to find, and most have been thrashed or in bad condition.
How's the bike hunting going OP?
Which 400s were you looking at?
I got an FZR 400 earlier last year with 12k on the clock and not a scratch on her for £1100. Not had a single problem during the 3k miles I've rode her. Also there seem to be ample parts on evil bay?
Also, particularly with the FZRs, I think you're getting a lot for your money. The 400s came with an aluminium delta box frame compared to the 600's steel frame. They have an exup valve, and the brembo brakes are shockingly good. Compared to my FZR 600 it's a much nicer ride, due to the racey feel and how easy it is to chuck round corners.
Oh and you will struggle to find a better bike around corners. The reason they're hard to find in good condition is because a lot of people use them as track bikes for this reason.
It really is worth finding one that's been looked after though.