Does anyone now the download size via Steam? Only reason I ask is that I am using a dongle and have to pay for extra bandwidth, but if I buy the disc I can install from the disc? Any ideas on Steam size cause I honestly cannot be bothered to go into town to buy it!

The size over the steam cannot be any less.

25 GB for normal version

+ something for x64
+ something for modding tools
+ ~100 GB for Super Quality pack in future

You need space and you should get the retail game.

This is a steamworks game, so it requires steam integration, buying a retail copy mean no problems with steam features.

I think Steam compresses data for transferring.