If you can, do the tests in a low signal environment, like a basement. The wider the channel, the higher the bandwidth, the higher the risk for co-channel interference :)
So depending on your deployment, walls, amount of clients and environment, the sweet spot is typically 80 or 40 MHz. 160 Mhz (which the 3800 is capable of) is rarely possible, because of the lack of enough channels.
Not to forget, your client also needs to be able to to 80 MHz (160 Mhz is near impossible to find, yet) and 802.11ac for the 3700 or 802.11ac Wave2 for the 3800 one.
In my case with an 802.11acW1 client and an 3700 AP set to 80 MHz channels, I get around 25-30 MB/s transfer speeds in Windows, tested with simple file copy (not very scientific, use iperf.fr for better results). With the same client connected to an 2800 (we don't have 3800) I get maybe up to 37 MB/s. This is in a crowded environment with the AP around 1 meter from the client. Your results may vary greatly. If I had an 802.11acW2 client, I might get slightly higher speeds.
For example, if you don't share the building with other companies and have thick walls, go for 1 AP per room with DFS enabled (if you have a controller in use) and set to "Best" for the channel width. This works typically great for data, but is probably not suitable for VoIP on Wifi.
