I tried HC-110 dil. D (1+39), 20 deg. C, 6.5 minutes with a very healthy pre-rinse.
I just hanged the negs to dry. They look a little thin but contrast is ok. Will try to give a little more exposure next time. Perhaps bump dev time to 7.0 minutes.
I've used the Efke 100 in HC-110 (1:50 from syrup) for 6.5min, and also got a slightly thin negative, and not that great of tonal range as compared to Rodinal.
My standard is now Rodinal 1:25 (as usual), but will up the time from my standard 6.5 to possibly 10. Efke has a beautiful tone when processed in Rodinal. I highly recommend it.
Forgot to add that also, HC-110 is my standard for Plus-X & Tri-X films. Has an unbeatable look, when shot through Zeiss, and printed through Schneider.