[MLB-WIRELESS] Yagi vs Grid

[John Briggs]

Has anyone had any practical experience of using a 15dBi yagi verses a 15dBi 
grid??
Diversity / Link reliability / alignment hassles etc.
Its a ~6km hop across suburbia.
On paper, 15dBi will only give me 7dB headroom (calculating 85dB reception 
for reasonable bandwidth) to a 8dBi omni the other end.
But I don't think I will get a larger grid antenna past the strata 
corporation which currently has a "no external antennas" ruling.
Worth trying the yagi??
Or will I need to put a 15dBi at the other end too.
-John