Deej, had it occured to you that there may be a problem with the engine, or it may be restricted??
Theres no way any 748 should struggle to top 120 on a flat road. It will never be as fast in a straight line as an R6 but the difference is not as great as you would think.
As for the handling, what tyres do you have on it? The choice of tyres can make a big difference to the turn in, I had BT012ss on mine, but D207RR Dunlops are highly recommended as well. Changing to these tyres will not upset the straight line stability either.
You can mess around with the ride height if you want, but I wouldn't bother as it will leave you no adjustment when you change the chain length, and that is what the ride height adjuster is actually for. Just turn the steering damper right down and get the forks and shock set up for you and your riding, and you will be fine!
Also, give yourself some time to adapt, it took me a year to fully get to grips with my 748 and that was coming from another Duke.
Final piece of advice.......
Don't listen to a word Weeksy says!