Dark is a pretty good way to describe the sound. They are not lively speakers...
I found that they sounded really really good with some amps, and not so great with others. I used them with some tube heads (fender and hiwatt), and did not like the way the responded with those amps, so that's why I sold them. They sounded great with an Ashdown Little Bastard, but that wasn't enough volume in the end. It's been a long time, but I don't remember really digging them with a Little Mark II either.
Sold one to a guy that was pairing it with a ABM 210 combo. Not sure about the other guy, but when I sold it to him, we made the trade at a music store and tried out the speaker with an Ampeg 7 Pro and a P-Bass. DANG. I almost didn't want to sell the speaker because it sounded so good.
Ashdown doesn't even list a freq range on the 6x10 or 8x10 cab. They are not the best about that.
Bottom line is you need to try it out and see if they work for you. If you don't have that option, then you just have to do the best you can. I am a fan of 15s, but a 410 would probably cover most everything, a 610 would for sure. Like Jimmy said - if you go with a cab with a better range, then it's your choice to dial the highs back.
Tom Bowlus has a cool thread on here that is a 115 shoot out. Doesn't include Ashdown, but he compares about 6 different 115 cabs. Might try doing a search for that.