Hello I just got my X99 classy all set up and I have a couple of questions as the manual is abit light on info so here goes, first I have a M.2 ssd Crucial 128 gb   and it was working on another motherboard (X99ud4) and the classy doesn't see it. And yes I turned on the slot in the bios. since there is different types and there is no compatibly chart for M.2 ssd's that I can find, can anyone help? #2 is do you need the 6 pin power connector on the bottom of the board for 2 way sli?

M.2 sata does not work in the m.2 slot. That is drive m.2 sata and the motherboard only accepts m.2 pcie. You require the m6e, xp941 or sm951. There are currently no other drives available the will work.

EVGATech_GabrielT
Hello lerb50
 
 
The board supports M.2 Key-E interface. Please read full information about the M.2 slots and how they work in the link I have provided below.
 
http://forums.evga.com/M2-Everything-you-need-to-know-m2232589.aspx
 

The 22x80 slot (between the PCI lanes) is key m, and the Bluetooth/wifi is key e.

Plextor M6e PX-G128M6e M.2 2280 128GB PCI-Express 2.0 x2 Internal Solid State Drive (SSD) - OEM.  Will this work on my motherboard as configured as a boot drive?( I'll clone the Kingston)

Samsung SM951 is for me most interesting device. 
Soon price will be around 300e for 500GB and could be excellent option for Windows 10.
250GB is under 200e now, maybe is even 250GB enough. 
No reason going on other models, when they offer best performance or Intel 750.

If there is a boot option that just says UEFI use that one.

Well I didn't enable uefi boot and it works. Will it be faster in uefi mode?

M.2 PCI-E SSD needs to be run on UEFI.  Yes, it will allow it to run to its advertised speeds.
 
Have read at this for a better understanding.