Using --load-balance to split 30% to hashco.ws and 70% to cryptoculture.net, the latter's showing overly high hashrate, like 750-880Kh/s, when I only have a total of 464Kh/s! Sometimes it does show the correct rate around 260Kh/s though. I can only assume that this is a result of the way cgminer does load-balancing.
Is this going to negatively affect me by giving me an unsuitable difficulty if it thinks my hashrate is higher than it actually is?
Vardiff is calculated on the server by evaluating your current share rate... basically, the displayed client hash rate has nothing to do with the difficulty rating and such.
The only negative effect you'll see in load-balancing will come from mining on a PPLNS-style pool. Since you're switching around, you'll never get the full benefit of your PPLNS shares.