Yesterday, 17:05
Yes, I know about Saukav too. I did not have time to do detailed testing of it, but I understand what it does quite well and it should offer compression at the level of Pletter (likely somewhat better than Pletter), while being fairly compact. I believe that its approach to adaptivity, with multiple specific decompressors offered, is an excellent way to increase the compression "for free".
However, I strongly suspect that a better solution must be available, most likely for 1K intros and definitely for 256b intros. I can explain what I mean as follows:
Suppose you are working on a 1K intro that uses Saukav and at some point you reach the situation where the compressed intro together with decompressor uses up all available space. Suppose that the average decompressor length is 64 bytes (this is the size of zx7b decompressor - the origin of Saukav). Then your compressed size is 1024-64=960 bytes. I do not know the exact ratio offered by Saukav, so I'll use Pletter's ratio of 1.975 as a guide. Hence, our intro is actually 960*1.975=1896 bytes long. Let us now consider switching to a better compressor, e.g. Shrinkler, which is LZMA-based and compresses at the level similar to 7-zip. Its ratio on the same small file corpus that I use for many of my tests is about 2.25. Thus, compressed by Shrinkler our intro will become 1896/2.25~843 bytes long (I should be saying "on average", but it is very annoying to repeat "on average" all the time, so I assume it implicitly). We saved 960-843=117 bytes, which may sound great, yet in fact is useless. The shortest decompressor for Shrinkler on Z80 is 209 bytes long, so we saved 117 bytes in data, and added 209-64=145 bytes in decompressor, i.e. lost 28 bytes overall. The point is, when you are making a 1K intro, Shrinkler will lose to Saukav (to ZX7, MegaLZ, to basically any decent compressor with compact enough decompressor).
When working with 4K of memory, these concerns become pretty much irrelevant, you can use Crinkler, Shrinkler or any other tool of your choice. But at 1K the ratio becomes less of a concern, as long as it is not completely dreadful, and decompressor size starts to dominate the proceedings. For 256b intros the situation is even more dramatic. I made one such intro using ZXmini (decompressor size 38 bytes) and found it (the decompressor) a bit too large. More can be done for sure.
So, looking at your graph, I do not know what is your target size, but for anything <=1K trust me, without decompressor size included, this data is meaningless.