Verisons of iwlwifi and firmware for my wireless card?

Although you say you are running 14.04, your 3.16.0-xx kernel corresponds to Ubuntu 14.10.

The driver iwlwifi is somewhat unique in that the pci.id, for instance 8086:4239, tells the driver the exact device and calls the appropriate firmware for the device in question.

I suspect the version: In tree means that the version is what was included in the related kernel, in your case, 3.16.

Here is where the firmware is available: https://wireless.wiki.kernel.org/en/users/Drivers/iwlwifi Your card loads 8.83.5.1 which corresponds to the firmware for an Intel 5100, 5300 or 5350. If you found an earlier or later firmware file and placed it in /lib/firmware, the driver is still going to call and use the same firmware it is written to use.

As you see, the firmware for your device is available in three versions; the 5.4.A.11 extracts to iwlwifi-5000-1.ucode; 8.24.2.12 to 5000-2 and 8.83.51.1 to 5000-5. While it is perfectly possible to download and extract these and place them where the driver expects to find them, namely /lib/firmware, the driver iwlwifi included in kernel version 3.16 is going to call and use only the appropriate firmware file: iwlwifi-5000-5.ucode.

As for the differences, I am unable to locate any change log. I assume each succeeding firmware version incorporates improvements and/or bug fixes.

As for the drivers, the usual way to get a later driver is to compile backports: https://www.kernel.org/pub/linux/kernel/projects/backports/stable/ Or, if you are brave: https://www.kernel.org/pub/linux/kernel/projects/backports/2015/03/13/

If, for example, you wanted to compile the iwlwifi driver corresponding to the later 3.18.1 kernel, download this to your desktop, right-click it and select 'Extract Here': https://www.kernel.org/pub/linux/kernel/projects/backports/stable/v3.18.1/backports-3.18.1-1.tar.xz Then, in a terminal:

sudo apt-get update
sudo apt-get install linux-headers-generic build-essential
cd ~/Desktop/backports-3.18.1
make defconfig-iwlwifi
make
sudo make install

Reboot and check the version with modinfo. It should read:

version: backported from Linux (v3.18.1-0-g39ca484) using backports v3.18.1-1-0-g5e9ec4c

Each time a later linux-image is installed, recompile and reboot.

I suspect, given your symptoms, that the difficulty is unrelated to iwlwifi and its firmware. You might check the log, specifically /var/log/syslog, at the time the drops occur.