If you re jet a bike... you can always get performance gained. Not in a huge amount without doing a full exhaust or at least a can. I will say from personal experience in tuning and a can that you will see a performance difference. If you get flat spots, check your needle shims and make sure they're adjusted right, and that your air/fuel enrichment is adjusted to the proper level. You should read the manual still and keep good notes on what you're doing with those carbs. Good documentation will help you a lot in tuning so you know where you started from and end up at in the end. Tuning carbs is a bit of work, but I'd do it myself if I were you. You'll realize how easy it really all is, and you'll thank yourself for getting to know your bike that much more intimately. But trust when I say you'll get a lot more power from your bike if you jet it properly and adjust and sync your way to new found power. Maybe also try a +2 degree ignition advancer too. Then go from there if that doesn't suit you. Or! Find someone on Ebay or some other classifieds website that's selling a full Fuel Injection setup from a 98 Gixxer 750. Take the airbox, throttlebodies, etc... Then from that alone, you'll notice once you ride and it's all hooked up right that your power will skyrocket a bit earlier in the powerband range.