(Speaker Configuration)...........(Cone Surface Area, approx.)
..........4x10..................................220 square inches.......
..........5x10..................................275 square inches.......
..........8x8....................................280 square inches.......
With all parameters being equal, a 8x8 should...(in theory)...sound bigger and move more air than a 4x10.
But, with the Henry 8x8 design, it will sound big in the near field, but it won't project out into the far field well.
For small sized rooms, (depending on volume levels), the Henry will probably work as a stand alone.
For medium to large rooms and louder volumes you'll need FOH.
I'd suggest you're getting a 8 ohm 4x10 cab and keeping your two 210's.
Use one 210 for rehearsals/small gigs, two 210's for medium/large gigs, and one 210 and the 410 for a 6x10 rig for loud volume and large coverage gigs.
And depending if your head will do 2 ohms, both 8 ohm 210's and the 8 ohm 410 just because!