You might try vector graphics. Whether it's faster or not depends on a lot of factors but it's worth a shot. I can lag out even my fairly capable machine when I start playing with ten thousand individually placed trees, or highly complex filter effects, but I don't have to worry about resolution until I do a final, high quality rasterization. A fully vector toolchain might be out but even moving your earlier steps over might help. It depends a lot on the details of what you are doing though. Grab a copy of Inkscape and see if it looks like something that might help.