Great great cab. Among the bests I've ever tried along with my SWR Goliath III. They sound pretty much the same. Except the 610HLF is a bit more massive in the lows, more surface area, enough as a stand alone cab.
This cab is more than a simple "in between" the 410 and the 810. The sound produced is close to the 410 with the "wall of sound" produced by the 810. If I had to chose between the 610 and the 810, I'd probably go for the 610. Easier to move, more dynamics, tweeter for slap and clean tone, open cabs for massive lows.
Note: Don't trust the Ampeg schema of the cab. it's not 3 chambers, but only 2. One for the sealed 410, and another one for the opened 210 at the bottom.
In between a 410 and a 810