Hi Bryan,
If Steve is correct that your PBH is 87.5cm, then you and I have the same exact PBH figure. I have owned both the 59cm MIT Atlantis and now own the 55cm MIT Atlantis. The 59 is a BIG 59. I was able to fit well but had less than 1cm of standover (with big 2.3" tires).
I sold it and later replaced it with the 55, which is a better fit FOR ME as a mountain bike. I am 5'-9" tall with very long legs for my height. How tall are you? The 59cm might suit you better in the reach department if you are lanky, but if you are wary of minimal standover then 55 or 56 might be more appropriate.
Feel free to reach out if you have specific questions since my experience might be relevant to you.
-Adam