For what it's worth: I have over 20,000 miles riding time on the VN750, both with the factory installed tire sizes and the oversized tires.
I can definitely recommend the oversized tires--especially for a new(er) rider.
The over-sized tires will give your bike a more stable feel. They also actually improve the looks of the bike, too.
I went with the 170/80/15 on the rear, and the 110/90/19 on the front--and currently I use the Metzeler brand "ME880" tires. These sizes still fit the bike just fine.
These tires have almost 10,000 miles on them, and look good for about another 10,000. The factory installed tires were completely worn out at 11,000 miles....
If whoever installs your rear tire has a bit of trouble getting the larger size tire past the bike's swingarm, just let some air out of the tire, until it clears.
After you put a few hundred miles on the new tires, install "Ride On" tire sealant in them. This is a great hedge against a flat tire.
Check out some of the other threads here (by using the "search" function above) to learn more about this sealant.
Last edited by theauhawk; 11-17-2010 at 10:48 AM.