I s this a good motherboard: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131701
combined with i5 2500k or i7 2600k?
I am also wondering which case of these two are the best
Antec Twelve Houndred v3
Cooler Master HAF X
Taking a look at it, the Asus should do just fine. Infact i was looking at it just a minute ago. Its got 4 ram slots, enough PCI ports, fits the CPU. one thing that i caught was "(Due to CPU behavior, DDR3 2200/2000/1800 MHz memory module will run at DDR3 2133/1866/1600 MHz frequency as default.)". Still not bad, you wont really notice.
As for a case, the Antec looks like it'll have plenty of ventilation. Really, most "good" cases will, since thats what the case really is for, after holding all your bits and pieces. TBH, if you like the case, and it has its fans in the right places (i'm not big on top/bottom ones as they are a quick excuse to build up dirt), then it will work. I usually choose mine based on aesthetic preference. I like roomie cases to cram in tons of LED's, but i'm sure that did hurt me on my last comp which only had 2 front fans, 1 rear, and no side. Looked pretty beast but dont do what i did.
Both those cases are great though, i just personally think the Antec looks "cooler" :disguise:
Last thought, just make sure to put the fans in properly. The idea is "airflow"; getting the air to move THROUGH the case... a commonly over looked aspect, or just outright done wrong.