The range is approximately the size of an arena (The orc at one entrance of the arena and his party/clan mate at the opposite entrance).
Party bufs used to have about twice as much range as OLs bufs, but now OLs bufs have a pretty bigger range, so maybe they're equal now.
If the OL is standing near the big stone in center of Giran, he can buff pretty much anyone who's in the giran square. Side alleys, though, are too far away, so my guesstimate would be somewhere around 1500 range.
I did some testing on my WC a chronicle or two ago, the range seemed to be 1000, which is the range at which you can see names above people's heads. The rule of thumb I tell my party members is that as long as they can see my name, they'll get the buffs.
You've got me curious though.... now I have to go test it.