Take the MSF basic riding course, you'll know how to ride a motorcycle vs. simply operating one. Full face helmet, preferably hi-viz, or at least white. Those two things will cut your risk of having an accident. The MSF course taught me to ride defensively, which was like work at first (paying attention to so much), but now its habit.
Used to have a Honda Silver Wing, back when it was a motorcycle, now it's the name of one of their scoots. Without luggage, it was the GL500C, water cooled, shaft drive, smooth as silk. It wasn't massive, but you could run the highway all day long comfortably, it's the closest thing to a perfect bike I've ever seen. Could cruise all day at 90 mph if you wanted to, and I often did.
Now I'm riding a Honda Nighthawk, a 250cc bike that's easier to handle and put in the garage between the cars. Not a very good highway machine, and you want off of it after 45 minutes. But it's a great commuter bike. Buddy that I ride with has a Suzuki Bandit, an 1100 cc bike that he got pretty cheap, and it's been a really good bike. In the range you've expressed interest in, a Suzuki Savage (650cc) may be worth considering--they don't command a premium like Honda or Yamaha, but they run like iron.
Just my opinion. Good luck with your purchase, and have fun putting your knees in the breeze.
