If you read the posts on this foru,, it's a general consensus that 8" tubes cannot do 1080p properly.
Personally I find that a lot of people go on specs alone, and never look at the actual useage requirements. I doubt you'll ever scan over 64 Khz, which is less than half of what the XG 135 can do in the first place.
Theoretically, the extra bandwidth of the 135 means it will show a bit more picture detail, but again, you'll never use it IMHO.
(See my post here on the XG/9500LC comments).
Curt