What I always ask my clients is the following:
1) do you need a new machine right now? Does the new machine have a feature you need immediately?
2) does your current system not fulfill your needs?
3) if you are in mid production, do not pass go
If you answer no to either of the first questions or yes to the third, wait till the answers change. That way you get the latest and greatest but also don’t compromise your current situation.
It sounds from your post that your are upgrading cause of technology change (thunderbolt). Wait on the new hardware and software then. FCP7 runs under lion so in my opinion (it is just an opinion) hold off. Especially with FCPX still sorting out and since your on FCP6 might as well wait and see. Squeeze a few more jobs out of the current rig and save your money for a kick ass rig in about 3 to 6 weeks (allegedly).
Thanks for your time, hope it helps.
Bill Chrisite
Technical director
Bithurler Inc