Building Gaming/Work computers

Well, my current situation is 1 computer in the middle of fine tuning, 1 computer is working but is low performance and I'm about to start building a new computer to kill my console, do great gaming and be good for any work I may be doing later. the specs of the one under tuning: Just upgraded to an Asus m5a99fx pro r2.0, the 16gb 1600mgh crucial ballistic kit isn't playing nice, so it will be replaced by an 8gb corsair vengeance kit after money is available, AMD fx6100 (bought a year ago), cooler master 212 evo, ocz 550W power supply, 1tb toshiba hdd, xfx 6450 radeon card. Its running Ubuntu and has been great minus setbacks from a recent upgrade. Mostly used for web and gaming.

My future build will be in a phantom 530 case with either an fx9370 or fx9590 with a kraken x60 and several fans. I'm debating between asrocks extreme9 mobo and Asus cross hair formula z.  My real question is whether I should get windows 7 for my new computer or stick with Ubuntu? Also, are crossfire/sli bridged video cards worth it and do they work on Ubuntu?

Why is the crucial kit not working that well? 

i dont see any reason for a motherboard upgrade. your Asus M5A99FX pro R2.0 can handle every FX8 core cpu just fine. so i would say just stay with that motherboard. i would say just upgrade your GPU and CPU.  R9-290 or GTX780, thats your choice, and a CPU, well depending on which level of productivity you working, but if its mainaly gaming. then a FX8350 is good enough. in video editing a FX9590 will maybe do a slightly better job since pistol also upgraded her 8350 to a 9590, but for just gaming it will not make a huge diffrence i suppose, noth worth the extra money.

About os your hardware will probably work better on windows, i would say buy  windows and make a dual boot option. so you can decide to use both, or use Virtual machines those run like champs on amd 8 cores.

Grtz Angel ☺

MisteryAngel- the Asus is what I upgraded to, and for whatever reason, this motherboard is just particular. Asus even has a list of what they call "qualified vendors (qvl)" . Its fine though, after the ram upgrade to a corsair kit, everything should be cool and then I have a 16gb kit for my new build.

The new build will be home to one of the fx 9000 series. I will replace the old low performance tower with the new rig. Right now, on my "tech bench, I have an Xbox 360 with a computer tower on each side of it. Above that are my 2 shared monitors. the good tower is plugged into both via dvi, the OK tower and xbox are plugged into 1 monitor each via vga. After the new rig is built, I will move towards upgrading my monitor situation and end up with 3 monitors for emersive triple screen gaming like eyefinity setups or such.