I have the v3
I have the v3
and it's build quality is the same as the black chrome V4, and ASPH that I previously owned. In other words, about 5x better than a typical CV, and 3x better than a Zeiss, in my experiences.
One ASPH 35 I had dropped 5 feet onto cement and ice and bounced about 5 times, still worked perfect, and a little trip to DAG it even looked new still. Don't try that with a non-Leica lens ...
The look between v3 and v4 is very hard to discern, but the v4 may have a bit higher contrast, though bokeh is the same.
The ASPH has a different modern look, and even flares differently - e.g. aperture reflections when shooting into the sun, has a modern cinematic flare behavior.
If the ASPH were the size of the V3/V4 I'd probably go for one again. Otherwise V3 and V4 are great and equal.
As folks realize the "King of Bokeh" hype for the V4 is just that - hype, the prices of the V3 and V4 should level out. The ASPH versions (of most any Leica lens) will always be touted as "best" because it is what dealers can sell new now ... plus, it's not a bad lens ...
Oh- and about filters, the V3 takes 39mm filters, but to use the 12524/6 rect. hood, the centering prongs on those hoods would need about 1mm filing for it to work, but I imagine it works better than the round 12504 vented hood. Also, the 12504 hood probably won't work over 39mm filters on the v3, unless ultra-slim, so plan on using VII/49mm filters in the 12504 rather than 39mm filters, unles like me, you just don't use a hood as it rarely flares from side lights like the lux 35.
The best 35 ever? the late pre-asph Summilux 35.
I own the Summaron 35/2.8 in both M-mount (M2/M4) and LTM, and I've handled the Summicron 35/2 v3. (BTW, the Summaron has the exact same body/barrel/mount as the Summicron v1 -- the only physical difference is 2.8 vs. 2 engraved on the aperture scale.) The Summaron is noticeably better built than the Summicron v4, in terms of solidity of moving parts, particularly the aperture ring.
I also own the Konica UC-Hexanon 35/2, and that's better-built and more beautifully finished than either the Summaron or the Summicron v4.
I've never handled the Summicron v3, but I'm curious about its build, as well as its comparative performance vs. the Summaron, v4 'cron and UC-Hex. (Idle thoughts of a chronic GAS sufferer.)
::Ari