I have some food for thought and an interesting bit of information worth knowing before you buy a M99 here in Canada. Whether or not it's an influencing factor for you is entirely your call. When the time comes you will not be able to re-barrel that M99 up here. It needs to be shipped back to Barrett in the USA. The barrel is hydraulically pressed into the receiver and apparently Barrett is the only shop in the known universe that can do the job. Today that may not seem like a big deal but if in the future, God forbid, there are any stupid restrictions placed on 50BMG stuff (again) you run the real risk of ending up with a Barrett boat anchor that can't hit the side of a barn at 100 yards. It's a shame that a guy can't spin a match barrel into the M99 because they'd sell like hotcakes up here if that were the case. Anyway, my suggestion would be a phone call to Ross at PGW or Rick at ATRS. Definitely not the most economical path but by far the best investment you could make into a 50BMG rifle as far as resale and service is concerned.
Now, if you're considering the M99 because the price is right and a re-barrel/service is of no concern to you then by all means ignore everything I've just said! Good luck to you....