EP140 instead of EP 90 in Differential

Does anyone on here run EP140 in their classic car differential? I have a 1965 Sunbeam and was advised that putting EP140 in the back axle instead of the Rootes recommended EP90 was a good idea. The thicker oil apparently helps older axles in some way.

Anyone do it or are there any downsides if I tried it?

EP140 would be very thick in cold weather. Probably better in a steering box. I'd stick with the EP90.

140 ( hipress), is by far the best oil for protecting your gears in the diff . Basically,thick oil had hugely protective abilities. Thinner or more modern synthetic oils,which are thinner,will probably give better mpg, because they produce less friction.
However,in terms of gear face protection, viscosity will pretty much always win,and it will likely be quieter,though some clever,low viscosity oil ,like Castrol synthetic diff oil have mega noise suppression!