Not that much, actually. Both were very, very good, with the differences being mainly in the presentation of the soundstage and not in tonal balance.
In my system, the TPC’s presented more focused and “precise” images that extended from the front plane of the speakers backwards and a slightly wider L to R soundstage.
The SPTPC’s gave up some of the focus of each voice within the soundstage, and thus narrowed the L to R perception of soundstage slightly, but pushed the soundstage slightly in front of the plane of the speakers and so created more of an illusion that the voices/performers were right “in the room.” While less precise, the images were more holographic, though. Soundstage depth was the same for me with both types.
Personally I opted for the SPTPC, but the outcome is very much system-dependent and, of course, depends on individual taste.
Blue Jeans Cable will send you both (or all three) types for a no-cost in-home audition. They keep a CC number on file and don’t charge you until you make your decision. you can return the whole lot within 30 day if you don’t care for them. But that’s a low probability outcome, IMHO.