I'll agree with you on the 5 inches... but I'm 6'6" and nothing is ever too high.......
Until you have to reach the bottom of a 55 gallon tank at over 6' high.
7" is the minimum for me to work in. My 22 breeder rack has 10" between each tank. I'm 6'2" and the top tank is a tough one. If it is hard to work on you won't take care of it like you really should.