That will be an epic trip, so jealous!!!!
You will def score waves in Sri Lanka in August, although the trades will probably blow the surf out by 9/10am so get into it early.
September is probably the best time to head to Europe for surf. I would recommend hiring a car if possible and drive from Bordeaux along the atlantic coast of France and then head into Spain. The ASP comp will be in Hossegor late September so the parties will be cranking around that time. 2007 i got a bit skunked for swell but 2008 was pretty epic by all accounts.
It is so cheap to fly places in Europe, you could possibly surf say a break near Lagos in Portugal in the morning, catch a flight on Ezyjet or Ryanair at lunchtime and head to Biarittz and surf there in the arvo.
Oh if you hire a car and manage to get a parking ticket like i did, just use your wind screen wipers, the tickets dissapear pretty quickly.
October should be sick through Sth America, you have timed this trip so well....you have definitely given me some ideas ahaha
Hope ya score mate, you have planned it out really well so you should, if not, they are epic countries that you are heading to anyway