Regarding my playing against Fairy-max at Sac Chess, I recall I played at a speed chess kind of time control for the first (4)  games, and I thought I was holding my own in most of them for a considerable time until I made shallow tactical blunders in each of the games that cost me a significant amount of material, and ultimately the game. I'm not that great at fast played chess (or fast played CVs by extention), especially against a computer, where psychology is also a factor for me, just being a tactically fallible human, and one who is getting easily agitated in his old age too. There is also that a 10x10 board is bigger to visualize and generally think about (than 8x8), and that Sac Chess must be more complex than chess in terms of tactics and strategy (much is waiting to be discovered, if the variant's played often enough).

I think I misremembered the (4) later games, which I played at a slower rate, and forced the engine to move after only about 2 minutes on a given turn. In fact I now think I just won 1 game and drew one, and lost 2. My misfortunes were always due to blunders, and the engine didn't see far enough ahead in the game it lost. I seem to recall that the drawn game was due to a draw by 3-fold repetition that might not have been clearly necessary. So, not much of a test of piece values.

I think I wrote in the Sac Chess thread long ago that I pitted the engine against itself for one game, and amusingly it came down to a pawn ending, but unfortunately where the winning side was two pawns ahead. A lot of tactics going on in that game, and towards the end the winning side swapped two or three pairs of pieces off just to force the pawn ending, even though it was already clearly ahead by more than 2 pawns worth. I doubted it was already calculating all the way to the point where it promoted a pawn to an amazon, as that was many moves ahead.

Also in the Sac Chess thread, Carlos Cetina posted a game where he decisively beat the engine; the game started off with the engine allowing the trade of one of its knights for two centre pawns. Although, Carlos didn't write what the machine's rate of play was like, and it may have been made to be just a bit too fast for it to play sufficently well. In any event, things got far worse for the machine from there onwards. Carlos is a regular player on Game Courier, and it seems to me he would have a FIDE rating of at the least 2000, if he were to play over-the-board chess seriously by itself.. Other than that, a lot (if not all) of the games of Sac Chess I'm mentioning had Fairy-max playing moves that seemed to me, as a chess player anyway, to be anti-positional, in that it would block its centre pawns with pieces, even very valuable ones, in the opening phase.

At the moment it's clear that my ways of estimating piece values are, as a general rule, less to be trusted than estimations derived from computer studies (accounting for Fairy-Max' choice of values, I assume), but that does not necessarily mean computer studies always get results that are absolutely correct, either. The conclusion of computer studies that a single B=N in chess is particularly hard for most experienced chess players to swallow, even though that feeling is based on books and top human player's philosophies. A computer equating a B to a N (on average) may regularly beat a world champion, but that particular valuation would seldom if ever prove to be why the human would lose any particular game to a machine, I suspect.