I mean I'm on the fence because I like talking/thinking about new cars... the only things I'd really to are C6 or 370Z, both of which would be more expensive and kind of marginally better. Basically getting a better interior and better brakes... I think I'll just keep the C5 long time.
And on that note I think I am probably going for 4.10s. One of the shops that specializes in diffs/ring and pinion in the area that @Detroit found is willing to rebuild the diff with 4.10s for $1500. That isn't including the clutch packs, but he said they'll replace those for $150 if I want while they're in there. So $1700ish all in for the rebuilt diff with 4.10s. I called one local Chevy , they of course want me to bring the car in, but he said the left side seals replacement would be around $575. Entire diff resealed for about $1100.
This seems like a no brainer decision to me... what few reviews I find on the shop are good, I put an inquiry into the local car clubs on Facebook to see if anyone has any experience with them.