For accessing more RAM while using GPU-passthrough you can use the "pciHole.start = 1200" and "pciHole.end = 2200" options (works for me and many others). I have successfully passed my Radeon HD6450 to Ubuntu (12.04, 12.10 and 13.04) using Catalyst drivers, Windows 7 (also had to install the VMware driver along with the Catalyst driver) and OSX 10.8.3 (using unofficial hack/patch) on ESXi 5.0. For sound I'm using a Terratec AureonDualUSB on an USB-controller on PCI-passthrough.
Config is:
ASRock X58 Xtreme (bios 2.90)
Intel Xeon E5606
24GB of some DDR3 ECC
Club 3D Radeon HD 6450 1GB (on passthrough, showing as "Unknown VGA compatible controller")
Gigabyte Radeon HD 2400 XT (on passthrough, tested with Windows 7 and Ubuntu 12.04)
IBM M1015 in HBA mode (on passthrough) with 8x 2TB Seagate disks (for my fileserver VM)
Crucial M4 128GB (for VM's)
Crucial C300 64GB (for VM's and ESXi hypervisor)
Creative X-Fi PCI (on passthrough, only tested with Ubuntu)