Hi Alan,
I've never used the Lux R80, but have used several 85 (ish) primes such as Leica M Summicron 75 APO & 90 non ASPH as well as Canon's 85's both L and non L.
Hand on my heart, my favorite 85 of all time was the Canon 85L and I still miss it's dreamy pastels even today.
However that being said, the ZA85 took a while to grow on me, I much preferred the ZA135 for portrait shooting. But as often is the case, space restrictions often dictated the use of the 85 in it's place.
I've since warmed to the ZA 85 and in particular it's size on the a900, often choosing it over the 135 just for it's compactness and weight.
In terms of IQ, it's hard to fault, some colour fringing on high contrast subjects as they move in and out of focus, but in general and normal shooting hardly noticeable if at all.
I use a Rokkor 58 1.2 with the matte screen on one of my a900s, and that's a bugger to get focus spot on. So I understand the frustration your having with the R80. I normally find it helps when I focus past the subject and bring it back into focus, my keeper rate with the 58 improved quite considerably.
Below are a few images I had taken this past weekend while messing around with the kids. Lighting was poor, but they may give you a feeling of the focus fall off. They were shot f:/2.8 @ 1/60