Should I crossfire 2 Radeon R9 290X or should i just buy one Radeon R9 295X2?
For what exactly? if you are wishing to get the most out of your money for a 4K Gaming Experience two R9-290s would be Sufficient. also take into Consideration you'll need a Durable High Quality PSU. Wattage Ranging from 850w to 1000w.
Two R9-290s is about $500+ Bucks right now. that is an absurd deal. on top of Having 8 free games that come with it.
You're definitely going to pay a premium for the R9 295x2 over 2 seperate cards, but you also get the AIO water cooler for it. The R9 295x2 will probably run cooler than the 2 R9 290x's (my top R9 290 is sitting at 83°C while playing a demanding game that scales well with crossfire) and you need a case with lots of space and pretty good airflow for the 2 cards as well. Power consumption wise they should be fairly similar, so that shouldn't be a huge concern.You also get 2 times the free games with 2 cards (and 2 times Civ Beyond earth if I see that correctly) so that's another plus.
With dual cards you get more free games and they should be quite a bit cheaper.
With the R9 295x2 you get cooler and more quiet operation under load, less space and airflow required, etc. Also keep in mind that you are supposed to use 2 8-pin connectors from 2 different +12V rails on your PSU if you get the R9 295x2, just like you would plug in 2 seperate cards.
If you don't already have a 290x then get the 295, it's really hard to keep the 2 cool, especialy if they are right next to each other, i have a fan makeshift to blow air inbetween the 2 so it doesnt throttle.