I don't know the full details, Intel won't say anywhere to anyone (and I mean biggest reviewers here). Question anything todo with power/temps in detail, they always avoid and run.
What I do know is 89A is the stock Core area limit. Even decent 3-phase solutions can provide that. Uncore is not supplied by 12v so you don't need to worry.
In terms of power, Lynnfield doesn't draw 89A at stock, not until TB kicks in so you should be fine as long as your temps are right and as long as the voltages aren't going too high (MB MFGs always mess this aspect up).
TB is an excellent concept. The only problem I have with it is, it increases voltage highly unnecessarily thereby limiting itself. If you customize TB frequency and voltage, it will work out much better, meaning, you should be able to gain max TB clocks on all Cores even after some undervolting (so you'll always be under 89A and hence always work at max clocks).