Hello, I want to do some worthwhile upgrades to my PC I built a few years ago. I already installed an SSD but would like to add RAM and upgrade the graphics card. I currently have 4GB DDR3 1066 installed. I want to go to 16GB, can I install 2x8GB or do I have to use all four slots (4x4GB)? Also, what is the best graphics card I should get for around $100USD? I understand that PCIe 3.0 is backwards compatible with PCIe 2.0 (16x) but I'm afraid if I get a too fast graphics card the CPU (i7-860) will bottleneck it. Currently, I have a Radeon HD 4830 512MB GDDR3 card installed. Motherboard is the Asus P7P55D, if that helps. Another upgrade I'm thinking about is a USB 3.0 expansion card. Thanks for any advice.