2d is harder than 3d...
I started to write one in DBC, i made a scrollable map with big sprites /=not tile map/, unit selection, buildings, fog of war, but I couldn't make a good pathfinding, and the fog of war ate 10 fps (in 800*600 the speed was 30 fps without FOW.) It was still an engine, not a playable rts. Then I stadted to rewrite it in dbpro, I made a new animation system /the animated sprite commands are unuseable/, but I had problems with the collision... (not pixel-perfect)
(Sorry for my bad English)
386SX, 2MB EDO RAM, 512kB VESA video card, 40MB HDD, 5,25 FDD