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I finally downloaded 6-men Syzygy, performed CRC, put them on HDD, and WDL tables additionally on a 128 GB USB 3.0 stick. I played several thousands games to have a feel about them with both Stockfish and Komodo, but here I will present only Komodo 10.4 results, as Syzygy is more flexible there ("Smart Syzygy" option to probe 5-men from depth=2 irrespective of 6-men Probe Depth). Playing games is the only option to determine strength here, as for different Probe Depths, the search tree is different. What I found is that if keeping all (DTZ+WDL) tables on HDD, 6-men (with many different Probe Depth values) don't give improvement over 5-men on USB, oftentimes performing even worse for small Probe Depths. Both give about 10-15 ELO points over non-Syzygy (for Probe Depth=24 from HDD) from endgame starting positions. However, with 6-men WDL tables on USB stick (DTZ on HDD), I got 35-40 ELO points improvement from Komodo with 6-men (Probe Depth=12) over non-Syzygy Komodo from these endgame starting positions. Here is some example run (gauntlet against non-Syzygy). It is also worth noting NPS and Depth reached as shown by LittleBlitzer:
"Smart Syzygy" was always "true" with 3-4-5-6-men tables. I would imagine that from SSD, the 6-men gains might be even more spectacular. With 128 GB SSD, it is probably advisable to put WDL on them. Also, with 6-men, my i7 PC (8 GB RAM) became almost unresponsive during some matches, due to RAM caching.

Another interesting test. From 6-men endgame positions, hard wins, I tested Stockfish dev and Komodo 10.4 without tablebases against 6-men Syzygy enabled Stockfish, to see how many are converted by non-TB top engines.

1s/move

Stockfish dev: +34 =66 -0
Converts 34/100, loses 0/100 won positions.

Komodo 10.4: +26 =72 -2
Converts 26/100, loses 2/100 won positions.

Without tablebases, even the top engines have hard time with hard 6-men wins.

Interesting results, thanks! BTW my test shows, that real ELO gain is about 20% of gains in endings (1/5 games is decided in endings) - so below 10 ELO from 6 piece then?

Jouni wrote:Interesting results, thanks! BTW my test shows, that real ELO gain is about 20% of gains in endings (1/5 games is decided in endings) - so below 10 ELO from 6 piece then?

If your 20% stands, close to 10 Elo points, right. But from entire set on SSD, could be 15 or so Elo points from regular opening positions.

Probing tablebases from SSD via USB 3.0 causes latency right?

SATA III is better than USB 3.0 for tablebases.

SATA or PCI-E is better for more TBHITS.

Nordlandia wrote:Probing tablebases from SSD via USB 3.0 causes latency right?

SATA III is better than USB 3.0 for tablebases.

SATA or PCI-E is better for more TBHITS.

I was not saying one has to put SSD via USB 3.0. I simply haven't yet bought SSD storage, so cannot play with those.

Are your 6-men endgame positions, hard wins from kirill-kryukov.com/chess/longest.../longest-checkmates.shtml? I have done some tests with them. Are you sure, that positions are really won with 50 move rule? I noticed, that even 5 piece positions with 5 piece syzygy ended sometimes as draw! 50 move draw from settings disabled (in syzy) didn't help.

Houdini 5.01 performs better in the famous Spassky vs Fischer endgame position if EGTB Probe Depth is adjusted.

I tried -10 and -5 on my brand new Samsung 960 EVO.

If syzygy is stored on M.2 SSD or equivalent, default Probe Depth is probably not correct setting for H5.1.

Nordlandia wrote:Houdini 5.01 performs better in the famous Spassky vs Fischer endgame position if EGTB Probe Depth is adjusted.

I tried -10 and -5 on my brand new Samsung 960 EVO.

If syzygy is stored on M.2 SSD or equivalent, default Probe Depth is probably not correct setting for H5.1.

What depth worked best?
I have a big SSD also.

Dann Corbit wrote:

Nordlandia wrote:Houdini 5.01 performs better in the famous Spassky vs Fischer endgame position if EGTB Probe Depth is adjusted.

I tried -10 and -5 on my brand new Samsung 960 EVO.

If syzygy is stored on M.2 SSD or equivalent, default Probe Depth is probably not correct setting for H5.1.

What depth worked best?
I have a big SSD also.

It's wrong to draw conclusions bases on few blitz games, but in my case -5 do seem reasonable.

Houdart argues that he don't like the speed penalty for probing tablebases, therby intelligent probing technique in Houdini 5.

For fast m.2 ssd, sweetspot is definitely between 0 and -10 somewhere.