Long story short, if you are buying anything over $300 for Grado headphones, the price/performance ratio you are getting would be worse than those of $1000+ headphones from other companies. Basically if you are buying RS series, for example, you are wasting money as much as you are buying HD800.
Really, only Grado you need to get is SR-60, SR-225, MS-1 (or MS-2) and that's it. Really.
Maybe GS-1000 ONLY IF you like classical and for some reason your ears cannot stand against Sennheiser and AKG headphones.....
Good post. I'd be interested in trying out a modded SR-80i, but aside from that, I would not recommend going any higher than the SR-225i.
The GS-1000i is nice, but at that price, I would always opt for an HD800.