In case someone else has or looking to have this setup...I checked my fax capabilities and everything works fast and flawlessly. To recap:
1. FIOS->VZ RTR->Cisco 2900G Switch->V-Portal->Fax/Phone
2. Using 4-wire cables for both Fax and Phone
3. Using HP's default fax settings (14400, Error Correction On)
4. I had someone at another location on the phone while they pressed send to test the speed and it was within seconds my line rung and approx. another 5-10 seconds the received fax was printed.
So far I'm quite pleased with my setup.