A couple months ago i decided to switch to UEFI and GPT because i felt like i needed more primary partitions. At the time i was running a popular "unlocked" version of A19 and MBR. However, i switched back to stock A19. After some work, i was able to get Windows 7 installed and dual booting with an encrypted Linux installation (LUKS+LVM). If i press FN+F2 to enable/disable the wireless, the laptop halts. It does this in Wndows, in Linux, and even at the Dell BIOS splash screen. This problem has been reported on this site in the past, but nothing recently. It is still an issue.
I mostly use Linux on my L702x. I have been keeping increasingly sensitive information on it, so i decided to encrypt the hard drive. The original partition scheme had already had reached capacity of the MBR system. There was a Diagnostics partition, a Recovery partition, a Windows partition, and lastly a Logical partition which contained my current Linux partitions. To set up the encrypted Linux i would need 2 primary partitions. I could deleted the Diagnostics or Recovery partition, but it seemed to make more sense to switch to the more modern GPT partitioning scheme where i could make as many partitions as i wanted. This, of course, also meant using UEFI.
In addition to the current partition scheme, at some point i had installed a popular "unlocked" version of BIOS A19. I didn't find anything worth modifying in the unlocked menus.
Trials and Errors
First, i made images of the Diagnostics, Recovery, and Windows partitions. I didn't bother making images of my Linux partition as i already had verified backups and prefer to restore from those.
Second, i reinstalled stock BIOS A19. I had done some research and found that it supports UEFI without the need for any "unlocking". My approach to this project was to make a "factory fresh" L702x but using GPT/UEFI instead of MBR/BIOS. That meant using stock BIOS.
I needed to install Windows before Linux. The trick i found to getting Windows installed was to install from a UEFI USB drive using Windows 7 + SP1. Originally i used Windows 7 without SP1, but this caused problems when installing the Dell drivers. There's a catch-22 in that in order to get to the internet to update Windows to SP1, you need the network drivers installed. Well, the network drivers want to install on Windows SP1.
After i installed Windows SP1 in UEFI mode, i decided to do a little experiment. I loaded the MBR Windows image on to the new Windows install partition. To my surprise, Windows loaded. Unfortunately, it would crash shortly after logging in. This began a series of boots into Safe Mode. First i disabled all startup programs (MSConfig) and then reboot into normal mode. If things seemed to work, boot back into Safe Mode and turn some startup programs back on. After many, many reboots, i ended up with with one program that, when enabled, would crash Windows shortly after login. That program was Quickset.
This now left me with a problem. If there is a start up program disabled, Windows will not run Windows Update. I thought simply removing Quickset would be an easy fix. Unfortunately, Quickset would not uninstall. I found some instructions on how to manually uninstall Quickset, but i decided instead that my experiment was over. I believe that if i had removed Quickset while still in MBR mode, i probably could have used the Windows image as is. However, as an experienced Windows user, i also know that Windows has baggage, and that reinstalling is usually the best option. In retrospect, i believe the Quickset problem is attributed to the problem in BIOS A19 as it has access to control the wireless device.
I did end up reinstalling Windows again. I had also made a list of the driver install order. I then downloaded and ordered them in advance using a numbered prefix on the folders e.g. 01 System Software, 02 Chipset driver, etc. One thing i found that i haven't heard mentioned anywhere is that some of the drivers have newer versions, but they aren't listed under Windows 7. Some of the Windows 8 drivers also install on Windows 7 and are newer versions. I forget the exact syntax now, but they were identifiable by their file name as it would include a Windows 7 reference, e.g. A12345_win8_win7.exe. I would be nice if Dell went back and updated the Windows 7 drivers with these that are newer and compatible with both.
GPT and UEFI are doable on the L702x. You don't need any special BIOS. The trick is to set your drive to GPT and then install using UEFI media. It seems to work just the same (i haven't noticed any increase or decrease in performance). The only drawback i've found is that you won't be able to use FN+F2 to control your wireless device. You must always do this from within the OS.
It can also be tricky to boot into the operating system you want if you're dual booting because you need to hit F12 to get to the boot menu and the splash screen can go by very fast (and boot you into the default OS).