remenber gentlemans,, the less frecuency in hertz the more signal travel along ,, for that signals in 2.4 band covers more distance but has more noise, 5ghz travels less along ,, far... less but less noise, the trick with 5ghz is the power inserted for transmision, thanks and excuseme for my poor english.i have 3x120 degree sectorial 2.4ghz 15dbi antennas and with 60+ clients working great. I have clients connected till 4km with 15dbi grid antenna with a good rx signal. U can get -70 or better with this config on 5km i suppose (with 15dbi grid). I think that there is no need to spend much money to build a very good system(and more expensive on client side to) when u don't need it. 2.4 fits your needs for the radius of 5km.