Well, you could start by at least picking something within the same ballpark. The Cisco's start at a little under $1000 each, while the UniFi HD goes for $349 each, but I'd argue that a UniFi nanoHD ($179) or UniFi Pro ($149) would be better with their higher max speed.
Yes, the Cisco can probably handle more clients per access point, and is faster according to the spec sheet. But do you NEED 2402Mbps when you can get 1750Mbps for a fraction of the price?
Finally, I think you're multiplying instead of dividing with your math there. WiFi bandwidth is shared among all clients. Which brings up another point against spending that extra money on the Cisco, in reality it won't be any faster than the Ubiquiti because they will both be limited to the slowest client that connects to them.