Nice one Glenn, with three cats in the house getting cat hairs off is enough of a problem. I would suggest adding a touch of colour to your grey mix, Brown's or blues, simple back and white mixes can be very flat and dead looking, a slight (very slight almost invisable) touch of colour will breath life into the horse coat.
Talking about brushes, I am a synthetic die hard, but recently discovered Armaster Brushes sold from The Art Shop Skipton. Bought initially to use when sculpting but now they are my favourite painting brushes.
Cheers Simon