The 5400 pack is the same MSRP as the 4900 pack.
Regarding C ratings...
Basically, you can run a hotter motor using the 4900 pack as it can handle up to 122.5A continuous current draw. The 5400 pack can only handle 86.4A continuous current draw. Either pack will be a great pack, but the 4900 pack will hold a higher voltage under heavy acceleration. Honestly, unless you really want the extra runtime, the 4900 is a better pack IMO.