It has only been one day, but my concerns over the 87Us variable weighting are gone. I am only using that board at work, currently, so I won't be able to speak to it for gaming.
Besides being black, coming in low noise, uniform 45g was one draw of the 91UBK-S to me. If you've given the 55g a good thirty day work out and it still just doesn't float, then its ok that its time to get a weighting more attuned to your needs.