Bocknut: last chestnut beer

Many homebrewers tried to brew a beer with chestnut once. Chestnut are full of starch, malt will do the conversion, have good flavor and aroma, in fall you can find tons of chestnut and have a starch source for free...
I brewed a lot of chestnut beers, never had unforgettable beers, sometimes had trouble; anyway I give it a try almost every fall. I don't like chestnut in ales, high fermentation always gives an unpleasant sweet-like aftertaste, but I had better and cleaner results in lager. However, no beer to be remembered. Last winter I had something like 20kg of chestnut found in the trees, so I decided to give it another try.

19,0 liters (preboil 22,0)
efficiency  75%, boiling 90 min.
OG 1,060; IBU: 16,0; EBC: 30;
Malts:
  4400 gr Munich Malt, 1,037;
  100 gr Crystal Malt 120, 1,033;
  750 gr Chestnuts, 1,012;
Hops:
  24 gr Styrian Goldings, 5,7 %a.a., 90 min;
  2 gr Simcoe, 11,4 %a.a., 90 min;
  20 gr Saaz, 4,0 %a.a., 5 min;

A kilogram of chestnuts needs an hour or more to be roasted and peeled, and you have to add this to the total brewing time. Sparge was lower. Not stuck but slower than in a normal bock.
What is potential SG of chestnuts? I found 1020-1025 online. But if I consider stable my system efficiency (75%, and i keep it low) 1012 is the real calculated potential, using 750g of chestnuts (after peeling). If I considef correct SG 1025 as chestnut potential, this would mean a 70% efficiency, that would be very strange: I used the same pocedure as usual with no errors.
So, in my opinion chestnuts yelds very low sugars.

Another bad point is the flavor and aroma contribution: even in a clean low fermentation, with few weeks lagering, I can't find any clear note reminding chestnuts. Just a little sweety flavor, overwhelmed by malty and melanoidin notes from decocted munich and crystal.
So, no OG points, no flavor, no aroma contribution. Maybe I need more than 15 or 20% to sense chestnuts in beer, but it's crazy to spend all this time peeling 2 kg or more for 20 liters of beer...

Now that is all written here, I hope I'll remember to avoid chestnuts next fall. I will just roast and eat togheter with a pint of ale.