Every application/enviroment reacts differently with regards to networks, whether its wired or wireless, and as you say, larger files can take longer. Are the users tyical files going to be large or small, how frequent, etc. If you really wanted to design a network this should all be gathered and analysed first, however foer a couple of AP's it probably isnt needed. in regards to the 20Mhz going further, I agree, in the same way 5GHz doesnt propegate as far, but it has its uses with N equipment because its less congested/more channels.
Again you are ferering 80-90Mb, isnt this the wireless speeds? Once overheads, security, etc have been added, I dont think any manufaturer would argue against achieving a mucher lower throughput. I personallay havent seen any enterprise N kit with only 100Mb ethernet. If they do then the kit must surely be badged wrong as gigabit switches dont have 100Mb uplinks! When putting traffic on to the wired network you should be aiming to improve performance, rather than maintain or even impacting performance?
@ kipling, never used Ruckus, but seen the stuff and would agree with what you said.
@Simon, check which spectrum (2.4 vs 5GHz) your laptops operate in before buying any AP's, so you can match them correctly.
Just my opinion!
CraigP