Nothing firm. I considered 3 carboys of the same wine using Hungarian cubes -- one with medium toast, one with dark toast, and one with half-n-half. I've never used dark toast oak, and it would be interesting to see the differences.
One constraining factor is that my primary focus is keeping a pair of 54 liter barrels full. I have a 5 year plan to not make the same blend twice, so that I always have a variety. Depending on what grapes are available to me, this could be difficult to manage.
All experiments (and I love experiments) have to work around that. This experiment worked out as I had 4 carboys of 2nd run wine. My 2021's are FWK, so there's no 2nd run to play with. I had considered purchasing 3 FWK Forte kits -- make one with 2 week fermentation, one with 4 week, and one with 6 week. It seems everyone is crazy about EM -- let's compare apples-to-apples to find out what it does.
It just occurred to me that I could ferment and clear the 3 batches, and reserve 4 liters of each for testing. The remainder of the 3 batches would go into the barrel. I'd need extra top up (15 gallons for a year in a 14.25 isn't quite enough), but I have enough other wine lying around and don't fret about mixing an odd bottle of something else into the barrel. We'll have to see ....
My 2020's are Meritage blends -- #1: 66.7% Merlot, 33.3% Vinifera Blend and #2: 40% Merlot, 40% Zinfandel, 20% Vinifera Blend. I reserved 5 bottles each of the Merlot, Zinfandel, Vinifera Blend, and unoaked samples of #1 and #2. Next fall I intend to taste test all 7 wines to see what the differences are. Since I have 5 bottles of each, the plan is to do the tasting annually 4 more times. This is also a good test of the aging of the Select 900 series Nomacorcs.
Check back with me in 6 years for the results!