The last two you linked actually wouldn't work as they are for FM2 socket (AMDs APU A8,A10 etc....).
As for 990vs970 the difference comes mostly down to PCIe lanes so if your thinking of going x-fire it might be worth it, but really I honestly don't think the average user will notice the difference between the 970 and 990 when in xfire.
990fx - x16,x16,x4 (dual x16 for Crossfire/SLI)
990x - x16,x8,x4 (x8 x8 for Crossfire/SLI)
970 - x16,x4 (x16 x4 for Crossfire/SLI)
This article is a bit older, but has some interesting reviews on 990 boards http://www.anandtech.com/show/5714/990fx-motherboard-roundup-with-thuban-and-bulldozer-a-second-wind-for-asus-gigabyte-msi-and-biostar
Me personally I would take the asrock and put the $50 in my pocket or use it towards a faster GPU! Hope this helps.