Any size will do. The ammount of coolant it holds does not make any difference to the system performance or stability, in the end. A larger ammount will take longer to heat up, but subsequently it will take longer to cool down as well. So pick any res, as long as it works as an air-trap you're OK.
http://www.overclockedpc.co.uk/product_info.php?cPath=38_32&products_id=96 i want to get this size, but they dont give the option of which size barbs you get included. does anyone body know what size it comes with? .icecube
i contacted them, and there going to fix the problem later. i think ill get the 250mm as well. .icecube