millets rucksacks

I am going on a world challenge expedition to Venezuela and on the kitlist is a "rucksack with at least 65 litre capacity and an internal frame". If you have any recommendations It would be really appreciated as I need to get one fairly soon. I have found a couple on the internet. The first one is 70 litres but i am not sure if it has an 'internal frame', could you tell me? The second one seems fine but comes in either 65 litres (which I think could be too small as the kitlist is a lot of stuff and i need to save 10 litres for group items) and 85 litres (which could be too big!?), is there much difference in 20 litre size difference? Here are the rucksacks (the second one also comes in 85 litre):

http://www.millets.co.uk/product/101961.html

http://www.thearmystore.co.uk/acatalog/Regatta_Survivor_65_Litre_Rucksack.html#a198

Thanks a lot for any help