While I do notice a slight 'donut' on the L4 and the 2 L2's that I have, they have never been a distraction. Other (non-CPF) people even after being shown on a white wall, sometimes don't know what I'm talking about. My L5 does not have a donut to my eyes.
I never see the donuts in actual use and only think about them when white wall hunting or when I read about them on CPF.
I just got an L6 myself a couple weeks back and I love it. Mine is nice and white and bright and does display on the ceiling while sitting on the couch (four feet up maybe?) a small donut... well, actually more of a bright little cheerio. But at distance it has a nice spread with smooth bright center, and again, in use, at distance, my eyes do not see the cheerio.
Hope you like it!
Redd