Hi Buddy
This is a great post. Sounds as though your making great progress. Don’t beat yourself up with the backward roll speed wise, it’s one of the more tricky roll patterns and when you start to push the speed it will always sound choppy until you’ve master it. It’s a bit like the Alternating Thumb Roll or Square Roll if you play it too fast too soon you loose it.
When I was a beginner I was always encouraged to practice my roll patterns slowly no faster than 70bpm. And I offer that advise to you. The goal should never be to play fast as your learning, that comes later once you’ve gained some level of experience. Speed will come when your brain is ready to instruct your fingers to play faster. It’s important to LISTEN. Feel the timing.
To help you improve your backward roll patterns you should spend way more time on them than you do on the forward roll patterns which from your comments in your post you have already mastered. In the beginning you will experience periods of frustration at your seemingly lack of progress but you have to push through this. If you spend just 15 minutes each day practicing the backward roll over the course of two weeks you should have it pretty much nailed.
Having said that don’t turn your practice session into a chore, practice is about having fun and achieving goals. So don’t let the lack of progress on your backward roll hold you back, move through @BanjoBen 's learning track but also keep on with practicing the backward roll patterns you will need them later on as your playing skills develop.
Hope this helps, Happy Pickin