Is there a digital LE version of the game?
AFAICT the version from Steam (£40) is the 'Digital Edition' with the modified and LE car packs. Whereas CD Keys (£24) is the 'Standard' version with just the modified car pack. The LE car pack looks nice but do you want pay £16 for it now or wait until its available some time later.
http://www.projectcarsgame.com/preorder.html