m50b25: If you're connecting to a p2pool node, try specifying the difficulty by multiplying your hashrate by 0.00000116, in your case it should be something like  -u Vd8EUUAq...+0.001624 -p x. I remember having low bitrate for some of my 7970s with some algo on p2pool before and setting the diff manually helped, not sure whether it was scrypt-n though or some other algo, but worth a try. It's your worker name (VTC address in your case) + 0.001624 without any spaces. Another suggesting is to get rid of the config file temporarily, you've got a lot of stuff in there and not everything might work with vertminer, when troubleshooting like this it's better to just start with default simple settings, no config, just bare minimum command line.

m50b25:  You mentioned going down to 1030 on core speed, but have you tried going lower? If you haven't, try setting one card to 950 in vertminer, and move it up in increments of 10.