I think the 210XST spec's out as 30 Hz, and used a pair with various 5-strings for a while. It works, but subjectively I prefer 15" drivers in the mix. The 210XST cabs like to be pushed in order to sound best, and in the upper end of their volume range they like flat EQ, I needed to mind the bass EQ to avoid reaching some limits. I have since moved on to tuned-down 4's (DGCF) and a 210 + 215 setup. I think the pair of 210XST's hung with the 5'ers, technically, but I really didn't have much use for the notes below D. I also think the output of the 210's seemed to disappear in the mix with a pair of 210's in those lowest notes, although the "mid-neck" notes were very sweet, but kind of imbalanced to me. Let your ears tell you, and you'll only hear the right thing in your intended use situation, a few times if possible. I'm done with 5'ers, but it would be interesting to see what a 212XLT or a pair of them would do.