I have to disagree with the assessment of the lenses.
Just too much overthinking.
None of the above are bad.
None is perfect too.
Just get one within budget and go shoot some photos.
No love for a lowly Pentax 50/2?
Pentax 50/1.7, really one of the best out there for the price and size
50/1.4? -I really don't see why
40/2.8?
Here is the 40XS, so said with all the big theories out here that its not FF.
This one is f8 and I have a full size on Flickr, I'd say its totally FF usable.
f2.8 works with the high ISO for most cameras nowadays (in a dim market)......
DA*55 - taken by my friend
By design, its a 'portrait orientated' 50mm, so don't expect even corner to corner sharpness (esp wide open).
Used for its intended purpose it shines.
Yes, its on FF.