Any idea how hot the oil gets in the Focus when driven hard?

I would use a 5w-40 synthetic in the Cosworth.

http://www.opieoils.co.uk/c-656-5w-40.aspx

Out of those, the best ones are the Fuchs/Silkolene Pro S, Millers CFS/CFS NT, Motul 300V, Redline and Gulf Competition. The Motul 8100 X-Cess, Millers XF Longlife, Fuchs GT1 XTL/Supersyn, Gulf Formula G, Shell Helix and Mobil Super 3000 are good, cheaper alternatives.

Although it's a manual, it needs an ATF fluid and the best options are the Amsoil ATF, Red Line D4 or Fuchs ATF6000, although the others are fine as cheaper alternatives.

http://www.opieoils.co.uk/c-771-dexron-iii.aspx

Cheers

Tim