Your question is pretty typical of people in your situation, who are looking into riding, going to school, trying to save money, and don't quite know the lay of the land in the motorcycle world. First of all CBR600's and ninja 600 (zx6r), are not and never will be suitable for beginner riders. They are not practical for your purposes (thrift, transportation, ease of riding... etc), are insanely expensive to insure, and are only designed to go around a track fast, not comfortably, or practically
I had a motorcycle as my only means of transportation in college. IT WILL NOT SAVE YOU MONEY. Insurance, gas, maintenance every 5k miles, oil changes every 3k miles, new tires every 6-8k miles to the tune of $200+ each, and the inevitable drops along the way damaging $1k plastics. You will also need to buy a quality helmet, jacket, boots, gloves, rain suit, and saddlebags and luggage. You have to be a committed, experienced rider to realistically take on that kind of transportation choice. You will miss being protected from the elements.
A note on saddlebags, A backpack is helpful, but ultimately adds to the strain of riding. If a bike is your only means of transportation, then lockable secured saddlebags are absolutely necessary. End of discussion.
Simply put the most efficient bikes for commuting in college is either a ninja 250/300, cbr/250, CBR 500, Ninja 500/650 Suzuki SV650, and KLR 650. All of these options are fun, and cheaper than most to own, maintain, insure, and ride. They all have significant after market options and accessories can be found cheap. They use smaller, less specific tires that are much more cost effective than their supersport CBR600 counterparts.
A note on speed, Almost everyone thinks that they will control their speed when they begin. The fact is putting a race car in the hands of a freshly minted 16 year old driver is a recipe for destruction 99% of the time. There are exceptions, but they are few and far between. I never would have guessed I would be traveling as close as dammit to 200mph on my sport bike, but I did, because I could not resist the throttle. Fortunately, I pushed my limits after tens of thousands of miles of riding experience. Most do not have that restraint and end up going way too fast before reactions, reflexes, and real confidence are sufficiently established. The result is little crosses on the highway.
Speed is one of the most addictive aspects of riding. When you are learning, (IE first 10-20k miles) stick to a bike that is forgiving, not overly powerful, that you dont really care if you drop once or twice, (we all have dropped our bikes).
A half inch of twist on the right hand can be the difference between traveling 10mph, and 60mph in 1st gear of a CBR600, It is about 10mph and 25mph on a CBR 250. It doesnt sound exciting, but every single rider I know who started on a smaller, lighter, cheaper, less powerful sport style bike is still riding safely, now on much bigger, more appropriate bikes for their developing skills as a rider. The ones who started on the fast race bikes either wrecked and quit riding, wrecked and died, or just gave up riding all together.