At the moment I don't think there's much between DDR 3 and 4, so you more of 3 would be better especially on a cheap build. I can't really make any other recommendations as I generally only look a gaming builds, so I don't know which affordable GFX cards are any good, I've a 960GTX which is pretty awesome in noise terms and performs very well for the price, but that is £100 over your budget. To be fair with your specs 16GB might be a bit over kill, unless you're doing any video rendering or the like? The biggest general performance improvement any system can make is an SSD if you can fit a small OS one into the budget. An SSD will make windows faster than any CPU or RAM update.