RE 50mm Primes

Im thinking of getting a 50mm from Ebay - I realize the 1.4 FA is the favorite.

What about the M f1.2? - This is manual focus only - I am fine with this - but is the lens good/great optically?

What about the FA1.7? Is this as good or almost as good as the 1.4?

How much difference between these 3 lenses optically? I would appreciate some feedback.

Also, I al looking for the 77ltd but no one is selling this lens currently on ebay - I realize BH has it - but Im thinking I can get a sound lens optically and save some cash for it being used. Of course after the rebate the 77 is $575. But I cant spend this yet, how much would the 77 go for in ebay usually?

Any other primes I shuld consider? Pentax has too many primes for me to research on so I would like some info.

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Sinan