In that case: you don't want IOS249* v65280. The IOS is indeed downloadable by NUS as a wad...but it is a stub. It simply doesn't contain any code but the framework (it has a name and a version number...and that's mostly it). The whole reason of this IOS's existence is to get rid of whatever cIOS resides in 249.
Needless to say:
you won't ever need the official IOS249 (although some games with recent firmware may nag about updates if you have a lower version number installed in that slot).
The most updated version of the cIOS can be found
on this link (or rather: if you follow the instructions, you will get it).
*IOS...not cIOS. This version is not custom at all. it's made by Nintendo