I agree it is fun to play with as long as you know what sizes are really available, like you said.
225/70 on a 6" wide rim sounds like a real squeeze play for the tire, you may end up with excessive tread wear in the center of tread. I get that with the 285/70/15 on 8" rims, no matter where I set the pressure...it's just squeezing the tire's sidewalls too close together.
Maybe 205/70 would work better and still give a tall look...if thats what you're after?
As for moving up to 17", I used your Discount tire suggestion and found that 275/60/17 tires are available...about 30" tall, 11" wide.
And for 17" rear rims, I'd like to look into these further, but there is no info on backspacing here...price is decent, however.
http://www.discounttire.com/dtcs/whe...62701&pc=23201