So, I have a Carvin PB200 combo with a 15" speaker. The amp in the combo is dead and I don't use it anymore because i got a Mesa 400+ that I run through a GK BLX410 cab. But I want more.

I'm not much of a fan of the speaker that's in the Carvin combo now, so the question is, can I replace the speaker with something better and will it be worth it? Or is it better to just buy, let's say a GK RBH410?