those choices mainly depended on the websites in question.
overclockers is expensive but higher quality goods
komplett is cheap but limited stock
and scan is a good all rounder cheap but has a nice range of products.
the EVGA is a nice choice if you want to upgrade soon as you get a 90 day step up program. Which means before 90 days are up you can upgrade to a newer graphics card but only pay the difference between yours and the latest model. The PSU is a good brand and enough watts the antec 550W truepower was out of stock otherwise i might have chose that.
Now I haven't heard much about gainward but I did read an article somewhere lately highly praising its overclock ability. So that card could be a good buy and its cheaper than other well known brands. Again OCZ power supply its cheapish and reliable mainly chosen on the website not having a wide range to choose from.
Gigabyte make nice reliable computer parts whether its graphics cards or motherboards one of my favorite brands to pick. Its cheap and will do everything you want. The PSU is hiper who are from what I hear a very decent PSU brand and will be stable and provide enough watts for your needs.
All the PSU's I chose where module I think not a huge difference just means you can take out wires that are in the way. The only problem that could happen is the wires not being long enough to reach parts of the mobo but its rare. If you dont like the look of any of the PSU`s you could look for others on those websites Id recommend brands such as seasonic, enermax, antec, tagan, OCZ and hiper.
you could also go for Nukems suggestion too I haven't used Cclonline though so no idea how their service is. Although the is isn't much diff between the 7900GT and 7950GT maybe 4-8 frames per second in most games. His choice is very sound though also worth consideration. The choice is yours!