I thought the front has a little more travel than 4.5" your right about the rear. A Gixxer can go just as fast on a dirt road but you'll never emulate similar lap times without changing the triple clamp angles. You could shorten your chain and draw the rear in an inch....
I looked up an older model GSXR 1000 and 600 for random comparison and it shows both to have 4.9" travel front and 5.1" travel rear. I'm not out to prove you wrong but much of what you are saying isn't correct. If my NC had 100 more hp and dual front brakes, and more cornering clearance. I could easily run with the guys on 600's and 1000's. I can through the turns now, but they leave me on the straights bc the NC is so darn slow. The only other thing that hurts me on track is cornering clearance. The NC is not made for lean angles like sportbikes are. I drag kickstand, pegs, exhaust, plastic guards near engine case, etc.
I've owned a CBR900RR, GSXR 750, and a ZX10R, all ridden many aggressive miles. The 750 and ZX10R both had some trackdays under their belts too, so I have that experience to compare the NC to and the NC doesn't handle much differently in the corners despite it's weight and upright body position. What separates me from faster guys on the track is horsepower, brakes, and pure rider skill level. I have passed many bikes that has triple my horsepower in the curves, and out-braked them going into turns as well. However, I have been passed by club racers on R3's and Ninja 400's, which have similar power to the NC but the rider is extremely advanced. Once having the forks rebuilt with the gold valves and sprung to my weight, and maxed preload on oem rear shock, I can't say that the NC suspension is a limiting factor in me keeping up with the faster bikes. It's simply the lack of horsepower, brakes, and mainly cornering clearance.
You can skip to about the 2:00 mark in the vid, I don't run tire warmers and allow the first lap or two for the tires to get up to temp. In this particular vid, I was running a Pirelli TD front and a Michelin Power Cup Evo rear. When the Pirelli front wears out I have Power Cup Evo front to replace it with. That's my new favorite tire, plenty of grip and corner stability. Also if you see some guy completely smoke me and they are wearing an orange jersey vest over their leather suit, those are instructors and they are usually club racers that can smoke most anyone at a track day. Lol