I have a 40 Alpagon in a short barrel mount and an IQ180. I haven't had it long enough to have tons of experience with it, but I've shot a couple of jobs in Abu Dhabi, Doha, Kuala Lumpur and some personal stuff in Immensee, Switzerland to have a reasonable handle on it.
As one would expect of a new generation Rodenstock HR, it is superbly sharp. The Schneider 35XL that it replaces in my kit is noticeably slightly less sharp and tends to fall off from the centre quite quickly. My main reason for replacing it though is that the 35mm has a max of 4-6mm of usable shift due to the massive amount of lenscast with the 80MP sensor. Where my 60MP P65+ was useable with up to 10-12mm shift, the 80MP is not. With the 40mm Alpagon, I am back in the 10-12mm shift zone and LCC in C1 7 cleans up the files nicely. The 40 is a little bulky and a little heavy compared to the 35XL, but in my view, the performance is worth the penalty. I could have got the 32, but it is too close to the lens I use most, the 23HR Alpagon, and as I have my gear on my back for 8-12hrs a day on shoots (and no pet gorrilla to lug it), the 40, being much lighter than the 32, is a choice I am happy with. Also, the 32 with a centre grad (in my view essential with this lens) is so large, that mounting filters starts to become problematic. The 40's much smaller front element is a breeze.
To date, my observations of lenscast and falloff with this lens has me happy to use it without a centre-grad (I'm not sure if there's one available for it yet anyway). I certainly wouldn't dream of using my 23 without the CF.
Unless I am mistaken, the 40 is also the widest lens you can use with the new short barrel tilt adapter, which I view as essential for my purposes. I havent received my tilt adapter yet but will post about this when I do.