I did 7,600ish miles on my gen 4 in about 2.5 weeks and I didn't think it was that bad. It was bone stock, most of the time by the time I had to get gas I'd get off the bike and stretch a bit to help be less sore/stiff. I also had a tank bag I kept it soft so I could lay down on the tank if I was cruising on the highway for a bit.
I just picked up a Yamaha Stratoliner and I don't think I'd ever want to do another trip on a sport bike again. The factory bags are so handy and the riding position with the backrest and highway pegs are like riding a couch down the highway. Yet still handles decently enough. I never wanted to push my gen 4 too much when I was so far away from home, sure I went a lot faster in the corners than on a cruiser and you can definitely do tour on a zx10 but just isn't as comfy as a bike thats more made for that kind of stuff.
I would get a good seat, maybe some heavy bar ends to help reduce vibration in the bars if thats bugging you, some way to bring luggage with (i used a kriega combo pack with a tank bag) and a little cruise control thing is handy to help stretch out your right hand sometimes.