The SINGLE most important stat for the AO Final EDIT: I was right

I'll keep it simple. Federer v. Murray today for the Australian Open Title. Here's Federer's 1st serve percentage in all 4 of  Major Finals he played in last year. This is via ATPworldtour.com match stats.

Federer 1st Serve % Last Year 

Australian Open- 51% & 6 Double Faults (Sure it was 260 minutes, but 6 is still a lot for Fed) L

French Open  - 65% W

Wimbledon -    64% W

US Open -      51%  & 11 ( ! ) Double Faults  L

If Federer serves well, Federer will win. If not.....

UPDATE:  I was right. Fed serves at 66% and won.