The 5437 was only sold with the 2.4 Ghz cards so I am not sure if this will work (due to it being a non-OEM spec'd configuration), but the Dell Part number 9VVTM is the version of the Intel 7260 card that has both 2.4 and 5 Ghz radios (and is still a half height PCIE card that will fit your system). You can call Dell Parts Directly or search online for this card. Unfortunately I did not see it on Dell's site or I would provide a link.
Please note that I did not find documentation stating that this card will work (again due to it being a non-OEM config by Intel/Dell), so I cannot guarantee it working but I do know the card will fit in the slot. A safer method of getting 5 Ghz working would be looking for a USB WiFi adapter that has dual band support, but I understand if you want to try having an internal card.
If you do decide to buy the 7260 dual band version of the card elsewhere, make sure it is for/from a Dell system and it is a half height PCIE version of the card, because the 7260 also comes in newer form factors.