No, it won't help. The 1M range (ff500000-ff5fffff) is more than enough.
The reason why the D-Link resource is not getting assigned is rather
interesting: as Wayne wrote
Here is the D-LINK NIC:^^^^^^
# od -t x4 /sys/devices/pci0000:00/0000:00:14.4/0000:02:02.0/config
0000000 49011186 80b00117 00000011 00004010
which means that the device class is 0 (not defined).
And in drivers/pci/setup-bus.c we have
/* Don't touch classless devices or host bridges or ioapics. */
if (class == PCI_CLASS_NOT_DEFINED ||
class == PCI_CLASS_BRIDGE_HOST)
continue;
The short term fix would be to assign proper device class to D-Link NIC
using pci quirk...