Thanks for the input everyone!
My budget is around $300 - $400 USD, and I’m in New Zealand so eBay is about the only option since the local market for LTM glass is pretty much nonexistent.
I definitely don’t hate my chrome Canon 1.8, but weight is an issue, and the newer black barrelled ones just look a little out of place on a barnack (and seem to suffer much more from the Canon Haze issue). The lens itself is beautifully made.
I have an Elmar clone (Industar 50), and it’s pretty subpar. It’s quite low resolution and flarey, which is surprising considering it’s a Tessar. I feel like finding an Elmar that is much better would be almost as hard as finding a clean summitar.
I did look at the Skopar, but prices have gone way up recently and for that kinda money I’d probably prefer to get some clean leitz glass. I’m also concerned that it’d be too contrasty?
One thing about the Summitar - it's no lightweight, weighing about 210gm. I love mine, but I got lucky. Mine has perfect glass, but came with the front cemented pair about 40% separated. Fortunately I could repair that, so I got very lucky to find the lens, the dedicated lens cap, the SOOPD folding shade, and rear cap at a bargain. It is from '46, with the 10 blade aperture. I wouldn't say it has a lot of field curvature, but it has some. So, don't use it to copy maps. You won't really notice it otherwise. The collapsibility is a big plus, I use it on a Canon IIb and carry it hiking in a waist pack. The Nikkor I have no experience with, however I have / have had several Zeiss Sonnars and some J-8s (which can be delightful), Sonnars from that era will be a bit glowy at F:2, very sharp around 5.6 - 11. Fun to use in a dark bar or nightclub, at F:2 some veiling flare but a sharp central image, very 1930s. on fast B&W.
When I had my Summitar apart to recement, I gave it a thorough mechanical and optical cleaning, so no "Leica glow" - just a very nice lens with excellent smooth contrast and some serious sharpness especially in the central zone (the corners are just fine). Compared to a v2 Summicron, it's at
least as sharp in the center, but the resolution is a bit less even center-to-corner. At F:5.6 - F:8 they'd be very hard to tell apart. By far my favorite Leitz RF 50, and I've had or used Summarits, Summicrons, Elmars, etc..
The J8s are a crapshoot these days, a good one is really nice, but they seem to be hiding. Then there's the difference in focal length. I use my good J8 on a Zorki-S, and leave the Canon calbrated to the Leitz standard. I also have an Industar 22, 1957, original to the Zorki-S and it's a pretty nice Tessar, I'd say at middle apertures it approaches the performance of an Elmar, sharp with good contrast and detail - the I 50 is purportedly an improvement on the I 22, maybe your I 50 has haze, or is incorrectly assembled?