I have a pair of 4641's loaded with JBL 2242HPL drivers. They are pretty good units. Very heavy and with nice sound. Efficiency is pretty good too. These have a lot of head room and will get very loud. They do not do much below about 25hz but down to there they are very good. Unfortunately I will need to sell mine in the near future since I simply do not need them anymore and a pair of them take up a lot of space in storage.
I think this is a matter of what you want. If you would like more output headroom and slightly deeper extension over what your B380 offers a 4641 will do it. It is a bigger enclosure, tuned slightly lower with more port area, a bit more efficiency, a bigger coned, heavier duty driver and more xmax. I would skip the 3635 since the 2042 driver is not quite as good as the 2241H. My 2 cents.
