If you've got 50mb bb, definitely go for 200mbs ones.
The "200 mbs" ones are actually 100mbit each way; I assume the 85mbs ones are rated in the same way, so would be < 50mbit each way and limit the bb connection.
Also bear in mind that it's "up to" 85/200mbit in exactly the same way Wifi can be "up to" 54mbit... i.e. you won't see it.
Based on my experience of 200mbs ones, I'd be surprised if you saw much more than 25/30mbit each way with the 85mbs adapters, although I'm sure someone who owns a pair will know better.