I've been googling the site looking for the maximum safe temperature range before one reaches a lean condition while boosting but unable to find it. Does anyone know?

 

Say again? Are you talking about exhaust gas temperature? If so, the problem with EGT is that you can't tell whether your EGT is high because of excessive leanness, excessive ignition retard, excessive ignition advance, etc. They are pretty useless without a wideband imho. Tuning via EGT without WBO2 is playing with fire (no pun intended).

 

Temps are going to vary a lot due to where you place the probe. Best place would be in the actual header. That being said, if you are seeing temps over 1300 F you are probably running lean, and at the very least you need to figure out whats going on with your car. Hope this helps.

 

http://www.sdsefi.com/techegt.htm

Good article on EGT and tuning. According to it, anything leaner or richer than 14.7 to 1 will cool the EGTs. Like Neal said, they are pretty useless unless you have already tuned your engine properly and are using it as a warning gauge.