rear shock life estimate

[fredmeister]

Anyone know what to expect out of a set of Bilstein sport rear shocks? I have a set of the yellow sport shocks on my 911SC that are at least 10 years old, and have seen lots of track use, and Detroit's finest road ways for over 90k miles now.
I was wondering if there was a good way to test the shocks before purchasing new ones to see if they were in need of replacement. There are no leaks around the shock body, and the car does not bounce like a normal vehicle you would see with bad shocks, but it is hard to gage because the suspension is so stiff overall from the mods to torsion bars I have done.
What should you expect to see from a life/mileage standpoint from these shocks?
I did notice some wheel hop under hard acceleration and cornering at Gingerman Raceway this past weekend, and was not sure if this was attributed to bad rear shocks, a few real bumpy corners (did not look bad from the drivers seat), or if my differential was causing wheel spin since I have an open diff.
Looking for advice, don't want to disconnect the shock mounts to test the shock if I don't have to, but will if that is the only way.