There is no doubt that you are running higher risk of something going wrong with the older models so i would look into a 2007 or 2006 at the worst.
Pro and cons
Pro - e39 M5.
instant torque which is pretty much available throughout its power band.
still looks good.
Available in manual.
Cons.
Quiet a few cars had problems with their vanos.
Drop in performance in hot weather.
difficult to launch. You have to be a pro with loads of practice to get it to run 13.2@108 at the 1/4 mile.
Pro- E60 M5
Is the last M sedan from Germany
SMG means supershifting and not humanly possible to match!
0% error in shifting or downshifting.. Revs are always matched
launch control means you can launch it perfectly 100% of the time unless you have bad tires.
Power keeps building all the way to redline.
Handles and brakes better than the e39 M5.
Pretty cool when you say you own a V10 sedan.
Cons
Bad on fuel consumption.
lacks torque at low rpm so you have to keep downshifting to get it to roar.
The clutch will get worn out if you use launch control 10 times in European models. (American models launch at lower rpms which makes the clutch last longer).
Only available in SMG unless you live in the USA.
Would need to put your hand over your heart if anything goes wrong with the gearbox.
ummm lastly, will get bugged with the new superboy on the market.. the CTS-V.. Its soo annoying and the arguments are thats its the best just because its faster.. like duhh...
Im sure i have forgotten some points and i hope others can help me out here... Its already midnight and im feeling sleepy