So recently I went ahead and bought this http://www.newegg.com/Product/Product.aspx?Item=N82E16814202146
I later realized that there is a different 290 tri-x which is this one http://www.newegg.com/Product/Product.aspx?Item=N82E16814202143
they have the same specs but I noticed that mine was 6+8 pin and the other one is 8+8 pin and the exhaust vents were a little different. are these the only differences or am I missing something?
This happens quite often. You will see that despite something technically being the same model of a product, it may not be identical as manufacturers quite often make minor revisions to their product as time progresses, parts become harder to source etc.
6+8 is the standard 290 power delivery, so you just have a stock 290 with the Tri-X cooler, as where the other Tri-X has a custom PCB and power delivery. The only difference would be the 8+8 design should have better overclocking capabilities due to having a higher threshold.
Either way, they are both overclocked the same from the factory, so I wouldn't worry a whole lot about it.