If you like the stability of your 98 GTX, I think you'll find the 2011 GTI LTD stability greatly improved. My first rides (and first loves) were a twin set of '99 GTX LTD's. I sold those to move UP to a twin set of '07 RXT SCIC's. Power an speed aside, its just a huge move up in class, in terms of the ride. Its just a better product
Here's a comparison... the '11 GTI is longer, wider, taller, and heavier.
'98 GTX Length 123" Width 47" Height 37" Weight 635 lbs Engine 787
'11 GTI Length 132.6" Width 48.6" Height 44" Weight 745 lbs Engine 1494
That being said, as much as I enjoyed those GTX's I couldnt imagine going back. Keep doing your research until you're satisfied....
Good Luck to Ya