My son games wirelessly, and he's experiencing far less lag with the WGL-4500 than with our old Linksys WRT-600N, but that one is on FW 1.15 (mine is the v1.22 "guinea pig").
According to this link: http://support.xbox.com/support/en/us/nxe/xboxlive/getconnected/CompatibleNetworkEquipment/CompatibleNetworkingEquipment.aspx, Microsoft has listed v1.21NA as the Xbox Live firmware for the DGL-4500, but given the bugs we hear so much about, perhaps v1.22NA is better (v1.22NA is so recent, they may not have gotten around to certifying it yet). It reduced my errors by about 70%. The errors most likely have something to do with interference, perhaps from someone's cordless phone or baby monitor.