Sorry Dan, that's not the whole answer. Aircraft type does influence the RVR as does company (crew) certification. However there are local rules that also apply that we as flight crew never hear about. As you well know, all you see is the greens, until the gate appears out of the mist right in front of you. Quite magically actually...
London is the best all around Cat 3 operation that I have ever seen...
Cheers