I am not aware of any revisions to any routerboard model except RB850Gx2.
This was mentioned explicitly on MikroTik's newsletter no. 66.
http://forum.mikrotik.com/viewtopic.php ... celeration
RB850Gx2 with Hardware Encryption Acceleration
The RB850Gx2 devices are now shipped with a CPU that features Hardware Encryption Acceleration (serial numbers that
start with “5”). Combined with up to date RouterOS version (6.28 or above), you will now be able to reach 500Mbps with
AES128 encryption on this device.
I don't recall any similar revision on any RB2011 model (or any other for that matter). I could be wrong though.
Usually MikroTik will release any hardware changes (ie: extra ports or something) as a different model altogether.
Regarding the firmware you will definitely be able to upgrade to the latest version available. It's fully supported.
Regarding the RAM, I've only seen the opposite on one occasion. I got 2 SEXTANTs from the same reseller at the same time, and one had 32MB ram (as mentioned in the device's specs) and the other had 64MB (which was of course a welcome surprise/gift!).
In the RB2011 series only the 'L' models have 64MB ram. All others have 128MB ram.
You should check
http://routerboard.com to find all the details/specs of each RouterBoard model.