Well I think I'm just about there for a half decent shave, this is the practice razor I've been using:

https://tinyurl.com/ybwggvpc

I can't get any more of the tarnish off, but it's pretty reasonable after another 4/8k session.

The other cheap buys that turned up are rather better than expected, and already seem to have the bevel well set. They're too nice to practice on, so I'll have to keep an eye out for some tattier pieces.

https://tinyurl.com/y9ouhn35

So I can get back to shaving again, which I suppose brings this one to an end, thanks for your assistance guys.