I've run 2's, 21's, 4's, 41's, and 4v's. I have owned 4's, 4v's, and just picked up a pair of 41's. I would definitely go for the 41's and keep the 4's. I ran 4's then 4v's and back to 4's and ate my lunch on the sell of the 4v's. I ended up liking the sound of the 4's better in general with my rigs.
The 21's are nice but limited use. The 2's even more limited.