VW recommend 10w-40 semi for mine. i used millers 10w-40 semi for ages then one morning this winter i was topping it up and it came out of the bottle like treacle lol
i decided to move to 5w-40 millers fully synth, 5w to be that bit thinner for the winter. having seen both at almost 0*C, there is basically no obvious difference in how thick they are, but the thinner fully synth warms faster.
ive never been tempted to change the hot viscosity tho