I originally had it set to one of the bitcoin.cz regional servers, but it kept reporting dead, so ended up just copying the main one.
Meanwhile I gave up on slushpool, and had a go at Antpool.
Also lowered frequency to 325, just to see if it'd make any difference.
Over 1 7 1/2 hour stint;
Discarded: 15,344
Stale: 4,572
Rejected: 0
Accepted: 0
As well as having a secondary set to Ghash;
Discarded: 35,995
Stale: 207
Rejected: 3
Accepted: 1,064
And it's now reporting 1 "x" on chain 2.
Seems like it's sh1tful performance no matter which pool I try.