riptool, it's okay to have slip on and jet kit... got that direct from rep at DynoJet Research. You'll get gains from the jet kit being able to focus your carb better, and gains from the pipe for airflow and weight... a good installer can tailor the kit for your needs too.
I just got rid of a 98 zx6r with a D&D bolt on and a jet kit. I had it dyno-tested twice. The first time I got a 105hp max at around 12,000 (really good reading)... trouble was, the needle installed was too big for regular riding and the curve was VERY peaked. So I took it in again last year, and had them look things over, and they ended up replacing my needle with a smaller one. I was disappointed in the peak power. The engine ran much smoother at typical revs (4,000 - 8,000 rpm) but the top end "hit" REALLY disappeared. Dyno? Same dyno machine - 101hp at 11,000 rpm. 4hp loss from a NEEDLE CHANGE ? Hmmmm, doesn't sound right does it? The hp curve was almost linear though. (Kinda like a CBR Honda... boring) So I guess what I'm trying to say is that 97.3hp does seem a little low for a tweaked '98 - but keep in mind there can be minor variances for dyno machines, weather, tune-ups, etc. Also, even brand new same bikes can get different readings (tolerances from factory, etc)... I remember my cousin and I both had identical '96 ZX6R's a few years ago, bought same time, came to dealer in same shipment and everything, and his was ALWAYS a lot stronger than mine. Sucked actually...
All I know is that my '03 on order better be a strong one, I was one of the first in Canada to pre-order one, so that oughta count for SOMETHING. C'mon Kawi, be good to me !!! Looks hot, claimed 125hp at crank outta the CRATE ! Only 355 lbs dry ! Looks like sex on wheels too... hot damn I can't wait !!!