Samsung 850 Evo 1tb +alienware M17x r4 - gpt or mbr

I am getting ready to do a reinstall on my Alienware M17x R4 that has all standard Dell/Alienware parts with bios version A13 (dell version, not mod). The only thing that is part of what you could have got with this model is that the 680m is a "MSI" 4gb version and is running on the MSI bios which isn't UEFI compat (Major Thanks to @Raidriar for his patience in helping getting this card working - he started helping me in early July so more than a month Kudos, also the experts over at TechInferno and @j95 - I assume same person here on NBR, who with others have provided a constant flow of inf/drivers updates)

Okay I having been reading so many articles I can't really make sense of this.

First is the Samsung 850 Evo 1TB already a 4k/Advanced Format or normal?

GPT vs MBR - Supposedly GPT is more resilient and reliable. Also the memory block/transfer on the 850 evo is suppose to be 512kb and so various articles say to use GPT but it doesn't say why not use MBR with the 850 Evo (they confuse me over the uefi (due to Win 7 64bit boot off drive) 4k/512kb vs a standard non-uefi mbr.

UEFI - Since not all devices are UEFI compat and depend on Legacy support, how will it affect the parts of the original spec'd out Alienware M17x R4. For example a 680m without a UEFI video bios, what problems will be created, and what issues created for the CPU, NIC, etc.?

Specs
Alienware M17x R4 A13 Bios (Dell)
Will be running in Optimus mode!
MSI 680m 4GB non-uefi bios working in Win 7 64bit Sp1 non-uefi
Drivers are modded for 680m by the experts at Techinferno
3720QM Intel with Intel 4000HD
Samsung Evo 850 1TB (boot drive)
Windows 7 64 Sp1
60hz Screen (original installed with model by Dell/AW)
8GB System Ram
DVD, Realtek, NIC, USB 3.0 (Intel), - all standard parts that were available with AW M17x R4
SoundBlaster 3di Recon (software version - also standard part of the model)