That was actually an F3 motor that I'd thrown together the weekend before the race and was hand carried down. The rest of the bike was a bit of a dog, but didn't go too bad. Definitely annoyed the other blokes, which was why we did it.
I've ridden/raced 250's and 400's of all specs. I still hold the 250cc SP lap records at both the main circuits in Thailand (because they don't run the class any more
), but I could only get within a second of my 250 time on an SP/F3 ZXR400SP. It was fast without a doubt (75hp on the brake), but you just couldn't throw it around like the NSR. One major difference is that a lot of people can ride a 400 fast, but a 250 ain't as easy. The 400 is more stable and you can sometimes get away with being a gear wrong in the turn, or a tooth out down the straight, both of which are unforgivable on a rip-snorting 250.