I'm putting together my second hackintosh using GA-Z77-DS3H and i7-3770 with 8GB ram identical to the setup OP described. I am using an EVGA nVidia GTS 250 video card. I can't get it to boot from the USB stick at all! Here what I've done:
1. Purchased Lion Installer from App Store on a MacBook
2. Formatted an 8GB USB flash drive with MasterBootRecord partition
3. Ran UniBeast to install to the USB drive
4. Applied BridgeHelper 5.0 to the USB drive
5. Disconnected all extra USB devices, SATA devices from the target computer
6. Held F12 and selected the USB drive as the boot volume
7. I get to the bootloader where I can select the USB stick to boot from, but when I do this, I get the gray Apple boot screen for a split-second, then it reboots to BIOS and I can't do anything about it. I tried booting with -x, PCIRootUID=1, =1, GraphicsEnabler=no, yes.
Any ideas for me? Thanks so much.