I would certainly go with the 06 Gixxer, but it's your decision. It's totally updated with parts, including a slipper clutch. Call up some shops, I'd wager you could easily find a leftover 05 for no more than $8000. My buddy bought his OTD for under $8000 last May and I got my 636 for $8200 OTD, the next week.
How could your buddy think he could get what he paid for his bike after riding for a year?