I've nearly finished my project!
Well, don't forget Frost and Hail.
Anyway, I've went through Blitz. All but Blitz 2 is solvable at RR 99. Actually, Blitz 2 is very close to solvable but appears to be just out of reach. In the attached "Blitz2_RR99_FAIL" zip file, I included two replays illustrating a method that almost works but not quite. In method 1, I succeeded in containing the crowd completely, but I had to do it at a position where I can't complete the 8-builder bridge to the exit, because the bridge started too far to the right. In method 2, I shifted where I dig and build more to the left, so I was able to complete the bridge to the exit, but the position where I dug was not as "good" as method 1's position, and so one lemming leaked out and could not be saved. Basically, if the level had allowed 98% instead of 100%, or if the level had given you 12 instead of 11 builders, or if the level has the "better" terrain closer to the entrance trapdoor, Blitz 2 would've been possible at RR 99. Alas, as is, the level appears out of reach.
As for 100%, all levels which you can save 100% normally can all be done so at RR 99. This means 100% saved for all except Blitz 12, 15, and 16.
I've attached replays for a few levels of interest. For Blitz 8, note that on the right entrance, the basher must start bashing at a pixel-precise location (as seen in the replay) in order to stop bashing after the first obstacle. For Blitz 13, the blocker must be placed at the pixel-precise location seen in the replay, in order for it to be successfully freed later in the manner seen in the replay. [edit: found another RR 99 100% solution for Blitz 13. Now the blocker doesn't need to be placed precisely, but there are other moves in the solution that require precision]
