With my own A1200 I balanced the background between efficient and aesthetically pleasing by putting a 1 bit background over a nice copper effect. That way it looks good, doesn't strain the CPU and only uses a few k of RAM (med-res PAL, of course).
You can't have copper effects if you use a GFX card I think, but a similar 1 bit image at 800x600 would take less than 60kb of RAM. An 8-bit image at that resolution would take something like 500kb RAM, and a true-colour pic would take a meg and a half.
I don't know how patterns work, but I'm just saying you aren't saving a lot of RAM by using them (especially since you have a GFX card, so I'll assume you have 32Mb+ RAM).
