Feels like the Zachtronics Opus Magnum approach would fit very well to your game, if you ever expand the type of operators available.
Say, footprint would be a nice metric to compete with other players, also players can try minimize their type of operators. Think of modern ICs only using the same NAND gate for every logic gate imaginable.
Of course you can compare the number of ticks to finish the puzzle as well. (i basically quoted the entirety of Zachtronics histograms)