I think the relative "feel" of bearing assemblies is interesting! (That's the nerdiest thing I've said in a long time.)

You mention viscosity, but I'm really more interested in drag/friction/resistance (I'm not sure of the proper engineering term here, maybe "mechanical impedance"?) Like a few grams, I don't think drag matters to all but the most elite cyclists. But we don't let inconsequence stop a good debate here, do we?

I've noticed a difference in drag in bottom brackets. Cartridge units, especially new ones, seem stiff to me. I assume this is due to 1) new grease viscosity 2) possible friction/tightness in new parts/seals and 3) bearing preload. Some older cartridge bbs I've encountered seem more "broken in" and spin easier.

Overall, cup and cone bbs seem to have less resistance to me. They don't usually spin quite as smoothly though, depending on their quality/condition. I also suspect that many cup and cone bottom brackets aren't installed with proper preload.

If your bb feels dry you should probably lubricate it. As to Phill bbs, my guess is that two of their main benefits are longevity and maintainability.

If you want to nerd out more on friction: bb drag, cartridge bearings.