Yeah, it's generally slow, even for the letters to appear on screen. Bustout was fast, but it probably used the machine language like it says you can do in the advanced manual for BASIC.
BTW, does it use the same chip as the Atari 2600? They look alike, and are both called Television Interface Adapter, but the Atari sounds better...
I don't think they share any important chips, but don't quote me on that. I do know that the Coco uses a 6809 processor, whereas the 2600 is 6502-based.