Flap discs aren't really ideal for removing paint because they load up. However, a 40 grit will do better removing the bulk of the paint without loading up as bad, then come behind with an 80 to smooth the metal out a bit if you want. They do make paint removal wheels that are sort of like a real gnarly aggressive schotch-brite type material that work really good and will not remove as much metal either.
Likewise, depending on how clean your welds are, a flap wheel may not be the best tool, but rather a knotted wire wheel. They will be far more efficient at cleaning slag and small spatter bbs from the metal. If you're looking to grind welds flush or smooth ugly beads, a 40 grit will make quicker work of it, and then something finer to blend it in a bit if you so choose.