The DFI Lanparty nF4 Ultra-D has a PCI-express x4 slot, an additional PCI-express x16 slot (which I don't understand because it's a non-SLIable board, so having more than 1 PCI-express x16 slot is pointless), a better onboard sound "card", 2 more USB 2.0 ports and 3 more audio ports than the Infinity. Of course it's a little larger in physical size than the Infinity one (but still ATX size), doesn't include the COM and LPT ports that the Infinty version offers (which are most likely outdated and insignifcant anyway) and doesn't support RAID 0+1 (which I don't think is used often anyway).
Basically, the Ultra is the latest "revision" of the Infinty board, it would make more sense buy it than the Infinty.