I know this is an old thread, but I do have some thoughts about the categories for this!
I think the main thing that separates runs with 40 lines is the level, because later levels end up having a higher speed and so naturally all the top speeds will be levels 5-9. Personally, I like optimizing level 0 play, It's just more satisfying for me. I'd love to see a category split for 40 lines from level 0, or even 0-4 is fine by me as those are all the same speed. First of all, this would be a better incentive for people playing those levels which would be nice since it's kind of not super fun to get a really good time from level 0 and still be like 15th place overall. My best time from 0 is 1:23 (haven't submitted that yet tho lol) and I think that's just as impressive as the incredibly fast times from level 9 and stuff. Secondly, I know there's some hesitation for splitting the leaderboard too much which I totally get, but this wouldn't split it much at all. The top scores stay the top scores, there's just like 20 or so runs that are now funneled into a lower level category.
I'd just like to see some more love for the lower level speeds, and because there's not a ton of incentive to play them I feel like I'm the only person really trying to cut my times down. I know I can do better than 1:23 though as that was from height 0, so either way I'm still gonna keep going with it. Food for thought here is all!