Graphical packages rarely use GPU unless you're doing rendering, so I'd check if the packages you're using can use the GPU, also I would check if they're multi-threading otherwise buying a 4-core/8-thread CPU will be a waste of time and you're better off trying to find the chip with the highest clock speed and possibly not a dedicated GPU. No point having 8 threads running @ 2.2Ghz if it's only using one if you can buy a chipset that has half the threads/cores but runs at 2.5+Ghz.
IMHO you are probably better off getting the best resolution screen you can, don't worry about that size HDD as I doubt you'll utilise that if you manage your data effectively and you're better off making sure you have adequate ram and possibly a SSD in there for performance. Then if you really need more data just buy a 30 quid 320/500gb HDD with a USB cable you can bung in your bag. An SSD will give you far better raw performance in all applications than a 5400/7200 drive and also possibly extend battery life.
Summary - RAM check, better screen, possibly get a 120Gb SSD or such if you can live with that capacity on a laptop. 2x HDD and a 1600x900 screen would make me frustrated, esp at a 17" screen.
I've had no problems with ebuyer myself, also their returns policy and customer services have been great when I've had a dead HDD. Post sales service is always something you want.
BTW saw your sig - I'll have some 550cc injectors for sale shortly if you want them