I've even been impressed by their 8" combo amp's tone, I can image with a good amp that the 4x10s would do quite well. Ampeg's stuff colors the tone quite a bit and sometimes
they count on you using an Ampeg cab concerning certain amps. Listen to it and see what you think, could be a winning combo for you!
I'm also with you on used, most of the time I end up changing out as much as I can to new stuff when I buy used. Upgrading a cab isn't rocket science though, it's a very simple wiring job if things go south and they might end up sounding better in the long run!