AMD Northbridge help

[cloud1161]

Ok, I am in the process of picking a motherboard and I am not sure which northbridge I should get.  My CPU is AMD FX-4100.  I am stuck between a 970, 990X, and 990FX northbridge.  I really don't want to spend much more than $120 on the motherboard if I can help it, but at the same time I want a decent northbridge so I won't have to upgrade in 2 years or so.  To my understanding, the only real advantage the 990X and 990FX have over the 970 is that they support SLI.   I am not really sure what the difference between the 990X and 990FX is.  http://www.newegg.com/Product/Product.aspx?Item=N82E16813128510 this is the motherboard I am currently looking at.  I am not sure if the 990FX means it goes well with the FX series of processors or if the FX is just coincidence (I kind of just noticed that right now).  So yea, any thoughts or suggestions would be greatly appreciated.  Here is my CPU http://www.newegg.com/Product/Product.aspx?Item=N82E16819103996.  I got it on a sale for $90 which is pretty good I think.   This is my first build btw and it's been a rather longer process than I had anticipated (extra spending money is hard to come by when you have bills and school).