Odd how different people have different experiences.
For me 8.91 is very nearly perfect for my purposes, while 8.84 was virtually unusable (due to a particular bug which DID appear in earlier versions very occasionally, but was MUCH more common in 8.84). 8.91 is awesome, and probably the one I will stick with, as it checks all the boxes I need (there is no noticeable delay when splitting tracks as long as the overall track is less than about 65 or 70 minutes [if you get longer than that, it does start to lag, giving a 2 or 3 second delay before you can start playing again after a cut, but I can totally live with that as most of my vids are around the 60-65 minutes range]). The bug in 8.84 I was having was completely fixed (I won't describe it, it's too complicated, but it was very much a huge problem in the prior version which made it almost impossible to edit any sequence that exhibited that bug). Everything else just seems to work perfect, I have nearly no complaints.
Even putting in transitions (which has almost always caused delays when trying to turn on playback) is often nearly instantly ready to play (not always), and even when it's not instant, the delay is usually quite slight (on the order of a second or two before the program can build the preview).
For me, this is the best version you've released in a long time. If I had one very minor quibble, it's that I still get slippage with the audio on export to MP4. It's very consistent, happens to each and every one of my videos. They all slip by about 0.4 seconds (with the audio lagging behind the video). I just have to, after the initial export, pull the MP4 back into VP, disconnect the audio from video, pull it back that half second, and re-export. The re-export does not slip (not sure why, maybe because it's much simpler with no transitions or speed changes or anything like that). I do wish that particular bug would be fixed, and if it was, I would change versions again, but really, it's not that big of a deal, takes me less than 10 minutes to fix a video after export.
So yeah, for me, 8.91 is great. Funny that for you it's not so much. I know everyone's situation is different. I guess ya just gotta find the version that works for your purposes, and once you find a good one, keep using that.