Underpowering is as real as the Easter Bunny. I was considering getting a BH250 and ramming an 810 under it. That would be plenty damn loud.
4ohm 210s are another waste of money IMO. Speaker area gives you volume, not impedence. To be louder you want more drivers which Is why the pair of 210s or 212s are the go in my opinion.
Check out the cab chart at TCs own website. http://www.tcelectronic.com/bh250/
The big thing that ticks me off is that they don't make the BC410 in 8ohm, otherwise I'd have snapped up two of them and a BH250 already.