PCI-E x16, which is what graphics cards use runs at up to 16gb/s. USB 2.0 is 400mbps. Graphics cards also require more power (about 150watts I believe?) which the laptop cannot supply, even if it is plugged in. I would suggest upgrading RAM, but theres not much else you can do. If your laptop had thunderbolt, you can get an external enclosure and PSU for graphics cards.