does the length of a graphics card matter?

Solution
No it does not matter. Since the provided video cards are using non reference coolers, their design varies and length as well. I haven't read the specs or reviews of the 2 R9 270X cards, but typically a bigger card has bigger fans and heatsink, but some smaller cards are much more efficient and just as powerful. Longer cards also might have fitment issues if you have a smaller form factor PC case.
No it does not matter. Since the provided video cards are using non reference coolers, their design varies and length as well. I haven't read the specs or reviews of the 2 R9 270X cards, but typically a bigger card has bigger fans and heatsink, but some smaller cards are much more efficient and just as powerful. Longer cards also might have fitment issues if you have a smaller form factor PC case.
 
Solution
If I recall the reference designs have the heatsink overhang the printed circuit board. Non-reference, custom, pcbs made by vendors may differ in size.

There can be performance differences, usually in the form of overclocking or temperature control.

In this case I would lead toward the Gigabyte, because they bothered to list the clock speed (1050/1100). You might look around to see if that model of Sapphire has the clock speed listed.
 
Length sometimes matter, but not in this case as they should have about the same performance. Sometimes they are longer because of their fans. If I were you I'd pick the first one; because it's cheaper, includes BF4 and I personally like Sapphire more than Gigabyte when it comes to GPUs.
 
alright thank you! as for the size, my case holds up to a 12.5 inch so im pretty sure i can hold almost any card i wanted to. Power Supply wise, they both call for 500W and 600@W for Crossfire and mine is a 620W. Thank you by the way Eadlef for the reccomendation, i was leaning toward the free BF4 but i didn't want that to get in my way of losing out on performance.