After lots of searches and reading I think I have more or less answered my own questions, but anybody with first hand experience please correct me;
Bluetooth mic positions
Nobody was stating what mics they were using in terms Of The sensitivity- I've done handfull of these installs and found if you have a poor low sensitivity mic it's always going to be poo. The lower the db rating, the more sensitive the mic.
4 positions generally used for the mic:
1. Oem- in the dash itself to the side Of The dials, not a great position by many reports but could be OK with some shielding maybe. No idea what mics used.
2. Drilling a hole through one Of The unused switches and poking the mic through. Perhaps better position soundwise but no idea what mic sensitivity used. Does not look so great in my eyes.
3. Top of A- Pillar, good position by most reports except for verts.again no mic details. Sunvisor can get in way. Visable
4. Centre top of windscreen good position soundwise again, except verts, visible.
Cable fishing tool seems a handy bit of kit for the job
The bezel surround for hvac controls in lowest slot is Porsche part number 996-552-339-00-01C relatively cheap for Porsche at 4.30+vat The cubby hole to replace the CD holder (or tape holder if you are really retro) is part number 996 552 253 01 01C (28.54+vat) which might be useful when the lower cubby goes to swop in the a/c controls. There does not appear to be an oem solution to put the a/c controls where the CD holders are, which is a shame. Edit- unless you are handy with a milling machine like Alex
http://911uk.com/viewtopic.php?t=125168&sid=58cf42ec1f5845a0543031161e5a9e95
I'm probably going to try the oem position with a good high sensitivity condenser mic to start with and see how that works..