first I'll say this......the tires you have on your VN750 are tired! lol even with low miles on those tires, they are getting too old to ride on safely. so yeah, you've got the right idea and are looking for new tires. good for you.
many on here (my self included) have gone with over sided tires. for the rear tire move up to the next size and it will lower your freeway RPM's a little. it will be a tight fit, but it will fit on the bike.
I believe the sizes are;
stock rear 150/90-15
and the biggest that I know that you can put on the rear is 170/80-15
if it goes vroom or boom, I LIKE IT!