From time to time, the question of how fast the turbocharger
is turning comes up.  I recently saw an ad for one of these
Optical Laser Tachometers which measure up to 100,000 RPMs.
They are relatively cheap (eBay) and might be adapted for
the turbo speed  measurement.

http://www.reliabilitydirectstore.com/Reliability-Direct-TC811-Laser-Tachometer-p/rdi-tc811.htm

Joel