Rick,
My experience is the same as Scott's. The only noticable damage to the grass in my yard comes from the fixed rear wheels on the mower. That problem will be the same with turf or bar tires. Overall, I am glad I got the bar tires. After a rain, when the ground is soft, I know the bar tires are helping alot with traction. The only complaint I have is that, in muddy conditions, big chunks of mud stick in the treads and end up in my drive way. You probably wouldn't have that problem with turfs, but then again, you probably woundn't make it back to the driveway either. If you think you will spend much time on soft, muddy ground, especially on slopes, I would go with the bar tires. Just my two cents.
- Ken in Mississippi
P.S. There is an on-going discussion on turf vs bar tires that you might want to check out. See the the recent threads.