watercooling 2900pro

[woppy1]

how much of a diffrence would it make to get a full cover block over a single block would a single block deal with the heat of thi card these are the blocks im thinking of
http://www.watercoolinguk.co.uk/catalog/product_info.php?cPath=27_31&products_id=604
http://www.watercoolinguk.co.uk/catalog/product_info.php?cPath=27_78&products_id=627

thanks in advance for the replys