Prices of those SKS-Ms seem to be on the rise.  Are they reliable?  Easy to find parts?  Accurate?  Good investment?  

I would have to think that a factory-made "hi-cap" SKS-M would be a good, reliable gun, at least as reliable as the quality of the AK mags used. No reason why not.

That said; IMHO - I'd just get an AK and be done with it.

The beauty of the standard SKS is the pointability, reliability, and handiness of the 10-rd gun. No mags to lose, no drop-free dangers, easy to load fast with strippers,a bit less fast shoving rounds down thru the top.

I have mine working with an "in-place" 20rd Promag Tapco knock-off duckbill mag, utterly reliable - but a bit more clumsy than the standard 10rd mag. It can be considered "removable" like an AK mag, but my SKS is just a range-toy, so I don't care other than the space it takes up with the duckbill in place.

If I were to use it as a SHTF gun, the 10rd "fixed' mag would go back on.

I'm have the Model D that came with the awful "Planet of the Apes" stock.  I "Tapco fucked" the stock and never looked back.

I really enjoy mine and it is currently my truck gun.  It is as reliable and shootable as any other SKS.  I do miss the bolt hold open on this model.  

The trigger really sucks, even by SKS standards.  I'm not sure how I would ever replace this trigger group if it ever broke and damned if I can figure out how to get it apart to replace components.

But I wanted one for a long time before I got mine.  I like it and it's not going anywhere.

If you could find the original stock, would you be willing to part with it?