Agreed on that.

Good luck getting all those for what you want to pay! But you never know.

Well I use the Samyang on the K-1 and am very pleased with it, even the corner resolution is good (just compare to a Sigma!!) The Samyang won't focus lock as its a manual focus lens though there should be the confirmation focus beep. DOF is so great with these extreme wide angles almost everything can appear to be reasonably in focus.
I'm sure you must have seen some fantastic photos taken with these lenses. I reckon you're simply expecting too much by pixel peeping! I expect you could pay many times the price of these and get little extra in return, given the complexities of making extremely wide lenses. If money's no object, try another brand. I note the Canon EF 14mm f/2.8L II USM sells for around £2K, nearly 10 times the cost of the Samyang. I bet it isn't 10x better and what cost the camera you'd use it on?

JR wrote one of those reviews, perhaps he could add his take on it and clarify your concerns about the method of the reviews.

Edit: A further thought has come to mind, if you're using an extreme wide angle it's surely to cover a wide field of view. If your intended FOV is much less, rather than crop the wide angle, why not use a more normal focal length lens and fill the frame. Otherwise, have you tried the Pentax 15-30? It would cost less than a complete new system.

Are M versions where available OK?
The original K mount 20mm f4 for £150? If only! I can't find one for even double that (sadly I had mine stolen and have searched for a replacement.) I'd happily negotiate more than £150 for one!

Should have swapped it out under warranty, they're not normally bad.

This is ePhotozine's resolution test of the Samyang 14mm:


Full review: https://www.ephotozine.com/article/samyang-14mm-f-2-8-ed-as-if-umc-lens-review-1...
IMHO You'd be hard put to find an extreme wide angle lens with better resolution!

As to the 15mm Irix. Resolution test for that shows really good centre performance but just look at the edges unless its stopped down to f/11.


https://www.ephotozine.com/article/irix-15mm-f-2-4-lens-review-30126

However the 11mm Irix is the opposite:


https://www.ephotozine.com/article/irix-11mm-f-4-firefly-review-30678

Stop down with that and it goes off.

I would expect better results at the long end would be achieved by cropping an image taken with a more modest lens.

Where have you seen that? Not in this thread!

Just to point out, black cameras don't take better photos than silver and black ones! Most of the early Pentax's had an Alloy top. I'd just get the best one you can find and not worry about that element too much! From experience, the black can wear off an make the camera look shabby.

If you can suggest your approx budget that may help with recommendations. As Peter says, an MX would be a good choice but a K1000 should be less costly. The MX being much smaller than others of that era. Probably best to examine the camera in person when you buy given you're looking at something 40-50 years old. Some are still good, others not so. With an MX, make sure the fresnell screen is in good order, they're removable and scratch easily and can get grubby easily too after which you'd be left searching for a replacement screen at around £30-£50.
Also, it may help to give an idea of the area you reside in as someone might be able to direct you to view a contender at a local camera shop. Remember, if you purchase second hand from a retailer, it should come with some sort of warranty. Buying privately you won't get that.

Tamron know Pentax users are connoisseurs so didn't believe this lens was appropriate for them. They'll no doubt team up with Pentax to make the Pentax branded super-duper version.

The examples on AP look very, very soft and only approved for Canikon users who aren't that fussy. Lots of CA and barrel distortion too.
http://www.amateurphotographer.co.uk/latest/photo-news/tamron-18-400mm-f3-5-6-3-...
Not a lens i'd want to purchase.