I am buying a new sistem from XPS 8100 from Dell spain (no XPS 9000 in spain) for GAMING, with an intel core i5-750, an ATI hd 5770, win. 7 pro 64 bit and ? amount of RAM at 1333MHz.
question 1: how much RAM do you recommend? 4GB is standard, 50 euros more is 6GB, and 100 more is 8GB.
question 2: the motherboard has 4 DIMM slots, so suppose I buy 2x2 RAM (so 4GB) and decide that in a year I will buy more. Since the RAM I already have is at 1333MHz (I bought it at that speed), can I upgrade with another 2x2 RAM but these ones at 1600MHz? So basically, can I have 2 different RAMs with different speeds working?
4Gb is plenty. If your doing photo-editing or video-editing then go for more. Yes you can but the 1600Mhz RAM would run at the lower 1333Mhz RAM speed and timings. Meaning you would not benefit from the 1600Mhz. Unless you overclock I think.
bsoon is right, You can only have 1 clock speed for ram which is set by defauylt to the slowest speed of the ram you have installed. I don't think you can overclock a Dell but that would work if you could.