Ideally it would be the same?

I've encountered a lot of material that advises if WU is less than 90% of your hashrate you should fiddle a bit with thread concurrency and intensity settings. It would be better to settle for a slightly lower hashrate with less rejections if that results in a bigger WU.

When I sum up my WU on different rigs, it is pretty close to the accepted hashrate as reported by middlecoin. So I guess WU is the one to look out for, not hashrate.