I had a chance to spend some time with a Heritage rig a while back. I'm not sure if we are ever going to run our full article regarding the Heritage head and 810, so here are some of the pics I took. For comparison's sake, that is a 2008 SVT-810e and my '74 SVT next to the Heritage SVT-CL and Heritage SVT-810.
The two cabs definitely sounded different. The Heritage had more low mids going on and was more smooth up top. The 810e had more upper midrange clarity.
Hi Tom, I had a great opportunity to compare a whole bunch of SVTs and 810s a few years back (1990 I think). I turned up at John Henry's rehearsal studio, and they had set up 2 or 3 cabinets and 2 heads for me to choose from for a tour. Some sounded a lot better than others (they were all very well used). Because they varied so much I got them to bring more out of the store room until I had 5 or 6 cabs and at least 4 heads. From this collection, I picked 2 heads and 2 cabs that I thought sounded best - and frankly, the ones I ended up with sounded awesome! The interesting thing though was that they were all the same model in theory, but they varied massively in tone and character.