Playing the game, I noticed on the 16x16 map, i didn't notice any FPS lag at all. Consistent at 70-80 FPS with a deviation of ~10-15
playing the 32x32 map the deviation was a little more noticeable, stuttering a bit to where the movement wasn't "fluid like." Average FPS: 60-70 with a deviation of +-20
playing the 64x64 map was worse than the 32x32, almost unplayable for me. bounces anywhere between 20-80 rather eradically, at one point when i got close to all the AI, it froze for a second and was down to 4 FPS, didn't get a screenshot though.
To summarize, maybe have a menu pop up or something or maybe a warning by the map options to let players know that their computer should be pretty beefy to run larger maps. I know my laptop isn't the greatest thing around, but i would say its close to par for computers out right now.
Laptop specs:
Windows 7 64 bit
first gen intel i5 2.2 ghz quad core
4GB of RAM
NVidia gtx 360M graphics, 1 GB dedicated memory running screen resolution at 1366 x 768