Try the A 50 1.4 but on 2.2( I know this from my FA 50 1.4 which is the same but with AF, it's strange but from 2.0 to 2.2 there is difference!) If you can close it down it is not so much worse than the M 50 1.7, It has 8 blade diaphragm and this makes the bokeh more rounded. The M 1.7 is with 6 not very rounded blades and for me personally the bokeh is weird
but the 1.7 is so much usable, I like it very much especially for night portraits and against the sun(it has very strong SMC!!!). You must try also Pancolar 50 1.8 MC(like a helios 44 but more sharper), Zenitar-M 50 1.7 - smoothest bokeh ever seen, Mamiya Sekor 55 1.4 - nice lens and sharp wide open.