You might want to work in a vector program in order to accommodate your scaling/zooming needs. Working in raster means that you have to have a really large image and for a world map that you want to zoom in on you're talking at least 10,000 by 5,000...in my opinion even that is too small, I like to do worlds at least 10,000 by 20,000 for my style. If you have a simple political map style then vector is the way to go but if you want detailed terrain then you need raster. Working in vector can keep the file size down thus less drag on the cpu but vector doesn't have a lot of the bells and whistles that we rely on from raster programs. If you have a robust hardcore gaming rig then it should be able to handle large raster images just fine or with a minimal chug. This is how I set up my pcs...if it's good enough for gaming then it's good enough for mapping. You can test your pc by just making bigger and bigger images and then start running a bunch of filters on things and see how long it chugs.