Depends on whether you're talking to a mechanic, or an enthusiast who makes a living working as a mechanic. Most working mechanics are trained (and expected) to set up cars according to manufacturer's specifications. To do otherwise would expose them to questions of insurance and liabilities. My turbo's base pressure is set to slightly below 6 psi. The "turbo lag" is noticeably less than the original factory setting. I've lengthened the linkage rod to set it back to the original 1.5 psi just for comparison purposes, and then shortened it back to the higher pressure. In our sometimes unpredictable society, few working mechanics ever get involved in high performance modifications. And even fewer would actually have the experience to do it.
Go to http://au.geocities.com/ozbrick850/engine-turbo-keithspage.html for the best description of turbo function and set up that I've found on the 'net. Have fun.

Marty
'96 855T