I'm in the same boat running a crossfire setup - 100fps+ in the field, 30-40 in the city/near atherytes. It happens to everyone - I've a friend running a Geforce Titan and even he drops into the 40's in these locations. Frankly, 99% of people who says they get a constant 60+ fps are lying to not only us but themselves right now (benching in an open field with no PC's around and getting 100+ fps doesn't count as an honest indication of performance). Also, the benchmark is more or less irrelevant tbh as although it shows you can play the game the performance displayed is inaccurate.

Its most likely the result of CPU handling than GPU raw power (trolls - notice I wrote 'handling' and not bottlenecking etc). Hopefully future optimisations will even things out a bit more.

Personally, I'm sat on the edge of my seat waiting for decent crossfire drivers - Although I love the high fps at times, Towns and Atherytes are actually running worse with crossfire enabled right now