it depends,
1) do the two NICs on your mobo support teaming (basicaly making them appear as one NIC
2) are you going to trasnfer to other GigE boxen on the network? if not, then no you wont see much diff
3) what kind of router is it? does it support jumbo frames / is it non blocking
if yes to all 3 then yes you will notice a difference. you will only be able to get 1gigabit/sec per nic, but as they are seen as one you will have a theoretical max of 2gigabits