This will probably be too much info, but I think that you asked an excellent question.
First, Big-T and moondog are dead on balls accurate.
First, since you already own a GSX-R 7 I probably don’t need to say much about it. Personally, I think that GSX-R 7 is the best balanced bike in the GSX-R line. The 1000 is great, but the 750 is the most impressive as an all around track bike. I have ridden a lot of GSX-R’s, CBR’s and Ninjas and the GSX-R 7 is still my favorite track bike.
Now, on to differences: The biggest things you will notice are stability and torque. The Hayabusa will be as stable at 160 as it is at 110, it is almost surreal. Most of that is due to the center of gravity and extra weight. To me, I like the Busa better in twisties but I am 6’3†and about 250lbs. Throwing a large bike from side to side is no problem for me. A good friend of mine here has an 05 Busa and is about 8 inches shorter and 100 pounds lighter so it is not as easy for him. But, the Busa was never designed to be a track bike. It was build to be a muscle bike that can beat just about anything on 4 or 2 wheels.
I like taking my Busa on short day trips. It is big enough and comfortable enough to ride 2 up and even at freeway speeds it is not uncommon for me to get 50+ mpg. The Busa is very solid and if you respect her, she will remind you that you are on one of the most powerful production sport bikes on the planet. But, if you are not attentive, she will punish you. I am sure you know that already though since you have a GSX-R 7.
I say, get the Busa. I just bought my second one and they are awesome.