Any comments on the Pen-F 20 or 25 mm's ??
I have the 20/3.5 and, even though I've just ordered the Panasonic 20/1.7, I know I'll be keeping the Pen F 20mm. From all accounts the 20/1.7 is an excellent lens -- fast and sharp with pleasing bokeh, not too much distortion being corrected in software, plus it has autofocus. Whereas the Pen F 20/3.5 is sharp with pleasing bokeh but it focuses manually and is more than two stops slower. Why keep it then? Because the Pen F lenses are marvelous. They feel like real lenses that are a pleasure to use. So that in shooting with them you can't help feeling connected to and appreciative of Mr Maitani's genius. (Which is also, conversely, why the current Olympus "Pen" lenses, far from paying homage, are actually an insult to his memory.)
Even more, the fact that the 20/1.7 is faster and easier to focus doesn't necessarily make it
better than the 20/3.5. Last month,
Mike Johnston wrote a post about a documentary movie called
It Might Get Loud, a group portrait of three guitarists: Led Zeppelin's Jimmy Page, the Edge from U2, and Jack White of the White Stripes. For Mike, the best quote in the film came from Jack White: "The instrument should get in the way. You have to pick a fight with the guitar." Similarly, the Pen F 20/3.5 makes one work a little harder -- and that's not necessarily a bad thing.
As for the 40s: I have the Pen F 40/1.4 and 42/1.2, the Nokton 40/1.4, and the M-Rokkor 40/2. As Godfrey noted, the Pen F 40/1.4 is slightly larger (i.e. physically longer) than the Nokton but it's also about an ounce lighter (165g vs. 197g). Both Vivek and Cindy have mentioned the most important difference: the close-focusing distance. Although I very much like the way the Nokton draws, the fact that I can't get closer than 0.7m drives me crazy. So I'm about to sell the Nokton. The M-Rokkor I'll keep, partly because there may be a Leica M-mount camera in my future, mainly because I'm a 40mm-holic and I always wanted to own a copy of this legendary lens. The Pen F 42/1.2 is, as Vivek said, as good as it gets. (I bought my 42/1.2 after asking Cindy how she liked hers. She said she liked it a lot.)
Executive summary: hold on to the Pen F 40/1.4 (which it seems you've already decided to do) and, if you can find a good copy of the 20/3.5 at a reasonable price, it's worth having too.