a 6 cores cpu is faster only if the program you work with will use all the available cores, in that case yes, way faster.
Btw, with the advent of the gtx 10 series, nvidia is not officially supporting 3 and 4 way sli anymore, so motherboards manufacturers are responding accordingly. It translates in to: no 4 way sli capable mobos in the recent x99 refresh (except for the asus rampage edition 10, but...600+ euro? LOL)
therefor, if you want to use the latest 68xx series cpu, almost any motherboard will need a bios update. If you can cope with a 59xx or 3 gpus it will be much easier
anyway, 4 way sli mobos :
On the cheap side you can get a Gigabyte : GA x99P sli - here a review :
http://www.hardwarecanucks.com/forum/ha ... eview.html it goes for 240 Euro, you may or may not need a bios update for Broadwell-e support (random, it depends on the revision, 1.0 will need the udate etc.) also i don't like the molex at the bottom of the board for the pci-e extra power.
Or asrock WS-E or (model 10G if you need uber/double/bruce-lee ethernet ports. this one is my favorite
) it goes for 400+ euros, it is durable, most of the components are server grade, it supports broadwell-e with a bios update...and molex again -.-
Or EVGA FTW K - again bios flash for broadwell, feature packed, very stable, average bios.
Or Asus X99 WS need a bios update as well fo broadwell, no molex here, just additional 4 pin power cable. Simply one of the best mobos out there. Be aware of the horrible asus RMA policy/service tho, in case of problems (not joking, asus = no customer care) same price range as the asrock ws
Or Supermicro....something, just dig in their website, among the plethora of models you'll find one.
some mobos can be flashed using an usb stick, you won't need a cpu to be installed. Some other won't even reach the bios if ther's no compatible cpu installed, in this case if you don't have a 5xxx chip at home, i guess you'll need your reseller to flash it for you. Do some research for each model. Also consider, all the above mobos are pretty old (i think the most recent is the Gigabyte) so on some models you won't have the latest goodies, usb 3.1 and type C, thunderbolt etc.
if you decide to use a 5930k instead of a 6850k you can use any of the above mentioned mobos without any bios update; broadwell is slightly better then haswell when it comes to ipc. Haswell is 100$ cheaper, is older, bigger die size, almost same power efficency, and is a better overclocker (according to tom's HW); but still you are getting an old gen processor.
i hope it helps.
Cheers~!
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