Hi, I've been working on fun sim game since C3 came out. It's isometric but only on one level, no height. My maps are 25x25 tiles in size. I've found thats the limit for my 10 year old computer with all the other sprites needed, and that works fine for my game. Also not having collisions on helps.
If you wanted to have 256x256 you could store all the info in an array then create enough tiles just to cover the screen then when the screen is scrolled the tiles stay in place but simply change the image of the sprites to the relative position in the array.
Sorry i don't have a more recent gif, this is quite old now.