I've recently moved from Jacksons to SP-Teris. I was mostly happy with my Jacksons, but there were some minor issues and I wanted to try something different. I was okay with the switch possibly being an expensive mistake.
In the Jacksons, I was wearing a C-width, which was the correct width for the ball of my foot, they always seemed a bit roomy. I couldn't wear tights with the skates without my feet slipping somewhat inside the boots and generally wore smartwool socks instead. I had issues with my heels moving, and had I stayed with Jacksons, I definitely would have ordered a split width. I was afraid, though, that the heel wasn't the only fit issue, and that while the width was correct, the boot just had a little too much volume for my foot. It may be worth noting that I was originally fit in a 10C in the Jacksons, but I only wore those for a few weeks before I knew they were too big. The fitter hesitantly ordered me a 9C and 8.5C to try after that, and even though the 8.5C was hard to get my heel into when fitting, that's the one I chose and that's the pair I'm talking about finding too roomy.
I had my feet measured for SP-Teris by a local rep and we sent the measurements to SP-Teri. They chose a size based on the measurements--a 9.5B with C ball. When they arrived, they felt like boats. The fitter encouraged me to heat mold them and try them on again, see if I could tie them tighter, etc. I did this for about a week but they still felt wrong. It happened that about a week or two later, I was going to be in San Francisco, so I brought the skates with me and paid SP-Teri a visit in person. George Spiteri took one look at the boots on me and knew they were too big. I tried on a few other things and checked the measurements from the fitter (he got the same numbers!). We decided to exchange them for a 9.5A with a B ball. When those arrived, they felt more like boots that belonged on my feet. It's not a custom boot, it's just a combination last. I don't know how many width differences they will do for the standard split width up-charge. My experience with SP-Teri was that they answered the phone every time I called and were able to satisfactorily answer my questions.
These boots have been much stiffer than I was used to, and at first my heel seemed to move, but since I've heat molded them and they've begun to conform to my foot more, that doesn't seem to be an issue. That was the opposite of what happened in the Jacksons, where the heel was initially tight and just seemed to get bigger and bigger. I'm able to wear these skates with tights. I also initially thought that I would need the pinky toe punched out, but now I'm glad that I did not have them punched, as they've definitely stretched to be just right. Keep in mind I've only been skating in these boots for about 2 months, but I'm at a point where I don't really think about them anymore--I mostly just skate. I'm happy with them so far, but they're still pretty new to me.
That's been my experience, and though it may not directly answer your question about the heel width, I thought I'd chime in. I'm happy to answer any other questions you may have about my experience going from Jacksons to SP-Teris.