We'll be ariving in FRA from PER at 5:40am hoping the get to Athens midday. So far, all I can find is an Aegean Air flight leaving at 18:00. Any ideas on better options ?

This is not a great idea, but it will work: Catch a morning flight from FRA to Cologne-Bonn or Stuttgart Airport and then fly www.Germanwings.com to Athens.

There's a Harpag Lloyd flight at 7am to Heraklion that might work ?

I don't think that gives you enough time in FRA to collect your bags then recheck them before departure to Heraklion unless your flight into FRA is exactly on time and there are no complications with baggage. Even then it's a risk.

Thought that might be a problem. I've almost convinced myself to change my flight from Sin to go to London instead of FRA. BA seem to have daily flights to Athens from Lon that would work in well.

Yes, and www.easyjet.com has very cheap flights to Athens from London, LGW, but at the moment you can't book with them beyond March, 2007.

Thanks brotherleelove, I'm convinced now, it makes my plans a whole lot simpler.
I'll fly into LHR, then to ATH with a minimal delay, be there around lunchtime. On the way back, I can fly direct from HER to LON which is great.

Brotherleelove told you about flights from Gatwick. You are flying into Heathrow. You need to allow about five hours for the change of airport.

A quick look at a travel booking site indicates that the cheapest and fastest connections from Perth to Athens are via Dubai (one change of plane and about 20 hours travel time.) London is considerably out of the way and would take much longer.