I have two MXs, a K1000 and a Spotmatic. I collect cameras, and I don't have a lot of b&w shots with the Pentaxes to show, because I mostly use subminiatures (Oly Pen F and minox) for film, just for fun. Mostly the 35mms are used for color negative machine prints. But I do have a couple I'll show below.
My lens selection for my Pentaxes are: 17mm f3.5 Tamron Adaptall, 35mm f2.8 Pentax-A, 50mm f1.4 Pentax-M, 50mm f2.8 Pentax-A macro, 90mm f2.5 Tamron Adaptall Macro, 135mm f3.5 Pentax-M, and a 400mm Tokina f5.6 ATX. I have others, but these are the ones I use.
This snapshot was taken with the MX and the 135mm f3.5, 1/125th at f11, I think, HP5 in HC110, scanned print. A friend of mine playing a sockeye in the Stellako River near Ft Fraser, BC.
The following picture is a hybrid, the original taken with the K1000 and the 90mm f2.5 Tamron, Tri-X in D76. Can't remember the exposure but it was indoors in a recording studio (this is the technician listening to the tape) so it was probably about 1/30 at f4 or so. The print was photographed with my K10D and the 50mm Pentax-A macro - before I had a scanner. The grainy effect is probably partially noise and partially grain, as I say, a hybrid shot.