I too would rule out the 310, the A70 is a marvellous little all round camera. It has essentially the exact same features as the A80 but minus a mp. The only other advantage the A80 might have over the A70 when taking tricky pics is the 'swivelly screen' allowing u to angle the camera awkwardly whilst still viewing the LCD screen, could be handy for your moving targets.
If however you will not be printing too huge, the A70 should be ok up to 12x8ish, then u might not consider it worth the £50 extra for the swivel screen of the A80. You alsoe mentioned about displaying your prints on screen, obviously the A70 will look perfectly smashing on screen as the additional pixel of the 80 would not be apparent.
In this range the canons really shine in my opinion.
I would go for the A80 budget depending, otherwise stick with the A70 out of your original 3.