Don't change the image, change the way you're using it. You can downscale it and use blur to make it look pretty. With my home connection 4 Mb is nothing, but I'm on my LTE router now and the page took about 30 seconds to load. The GTX doughnut logo is neat, but I'm not sure about the font. It's also way too big as of now, on my MBA's 1440*900 screen it takes over half of usable page space.
Next, I like that there's a mobile version, but the products page takes a lot of time to scroll through. Maybe make it a list with a smaller pic on the left and price on the right of it and make info come out on tap?
There is no way to compare builds at the moment, that might come in handy. Also as it's a WIP it's not a major complaint right now, but you really should put pics of finished builds instead of just cases. (also maybe throw in some builds just for doing stuff but that's not about the website anymore, is it)
Depending on who your service is aimed towards, the website is lacking a FAQ category. Why would a user go for SLI? Why would he choose to throw in an SSD? You know, casual questions.