Trying to decide between the Extreme Pleasure Hip 3 vs 4 for a second hip.

I prefer the form factor of the 3 as flat bases are not the most appealing and the 3 would seem to be amenable to more positions, however some of the reviewers have suggested that the 4 has a nicer internal feeling as well as tighter passages. So I'm quite stuck.

If anyone has experience with both and can give a specific comparison, I'd be grateful.