Softening ice cream with guar gum
Completely untried idea about efficient testing: You might be able to evenly divide a batch after churning, and stir a different, carefully measured amount of guar gum into each. (I'm not sure if you'd need to pre-dissolve it in a bit of cream). Then you could freeze them all at once, and test for texture. Hopefully your favorite ratio of guar gum will be less than or equal to the average ratio of the batches, so that you can then let it all soften and mix it back together (possibly with additional guar gum), and refreeze. If you're careful to not let it soften too much, you shouldn't have to rechurn it.