Will dont worry ! H81 motherboards usually have PCI-E 2.0 slots but all gen 3.0 cards work in gen 2.0 slots - PCIE is backward compatible . Just make sure your mobo has x16 PCI-E slot - 99.9999% sure it has
i would get i5 4590 for better performance and H97 motherboard-ATX or mATX .