You used the word sensible, Hmmmm 1.2 - 1.25bar IMO
I think some, maybe JB runs 1.3 on his UK ??
I guess since the limit of the MAF (A little out of my league here now) is between 18-19 psi then I would assume that you have to think about your fuelling if going over the 1.25bar mark ?
You also got to think about how long you want the turbos to last, give them more stick and it's natural that they will not last as long. (Turbo timer helps a little here)
As for location, I have seen a few with the to ID units taking up the space of 1 DIN, just below the single DIN headunit - assuming that you have replaced the stock Head unit ?
I have a pic somewhere....I'll have a look.
Anyway, I hope this helps.
I'm sure that someone will shoot me down if I am talking complete cr@p.