Tell us...
What statistics can you tell us about your terrain???
Are you using Terrain LOD and cashing????
Are you creating Model LOD's and if so are you creating ..._0, ..._1..._2 and ..._3 or are you using the LOD creation system in MED...
Same with your sprites... Are you using the _0,_1,_2 and _3 system???
What file size are your models??? And... what are the verticie count???
What type of files are the model skins??? The best that I found for frame rate is .dds files... they are smaller file size and render fast...

Please tell us what you are now doing to maintain Frame Rate and what your original Frame Rate was and is now...

Also... do you know that after you create the packed .wrs folder that your frame rate will increase????

Tell us where you are at and we will see what can be done...