Dont do it!
My advice, like many others, is keep the GS if you can, as you will inevitably end up wanting another one at some stage. If you're after something a bit sportier get a cheap CBR600 for the odd day when you fancy a thrash. I sold my GS1150 last year having owned it for a couple of years and bought an R1100S - great bike quick enough, tours, two up etc etc, but still longed for something for those days when you just want to take a leisurely spin out, irrespective of the conditions. So I bought an R80GS Kalahari(Basic) and find that I only take the S out on dry sunny days.
Hope this helps.
Pedro