Try the latest version of CGMiner (or BFGMiner) and let me know if you're still getting stales. Use US2 or US3 as well, since those are closer to your boxes than US1 is.
As far as NMC goes, Namecoin is falling apart... it's going to be disabled soon. If you look at the Namecoin list, they are almost all showing up as invalid. The whole Namecoin protocol for merged mining is a shambles and it's more trouble than it's worth.
I've updated cgminer, just to find that a new version came out, so I need to update again =)). Now it seems to run smooth, rejects are at usual level. Its sad to hear that nmc is falling apart. They could've used it for website certification, digital documents signing and just the obvious ID verification. But as we know, some of these can be provided by bitcoin. Its strange that your pool has lots of invalids for nmc, as bitminter doesn't. But bitminter experiences regular namecoind crashes, which affect bitcoin mining.
