I as I said above had the K9 GSX-R750. A very sweet bike, that toured very well, but I was a lot younger then, but that doesn't reflect to the ability of the bike. I did 1100 km in one long day ride (I was sore for days !).
One thing I can repeat here that the torque curves or HP curves (not quite sure now) show the 600 & 750 are almost identical below 7000 rpm. I think it is the torque, with the 750 making the HP up top of the range.
That annoyed me after purchase, as then the price was in Au $2000 more for the 750.
The 2 bikes are identical other than that, and I never went above 7000 in the use I did with it.
I test rode a 600 and was pleased with it, BUT opted for the 750 thinking I would get more lower down torque.
Unfortunately, Suzuki Aust. haven't for years printed the HP and Nm figures.