usually 990fx class mobo using higher quality of component..rather than 970 ..because 990FX intended to enthusiast class..
that's means, more overclockability, and more durable..
970 usually intended with medium user, which is do not really care about overclocking, and happy with the stock clock..or just slight increase of processor clock..
so, if you want to overclock your processor, get the best..not the so-so..
ASUS M5A99X EVO R2.0, is excellent mobo for the price..
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131874&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=
but if you insist with 970 class mobo,
this one will satisfy you..
asus M5A97 R2.0, this one have fair overclocking ability despite 970 chipset..
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131873&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=