Glad to hear about your MoBo deal. Faced with the same dillemma and opportunities, I'd have done what you did.
Your TurboBoost mode experience sounds about right. Those Xeons are locked down to any but the most conservative TurboBoost OCing.
I'm working with the 0503 BIOS myself, and with no problems I've not felt the need to risk it.
Here's the info on the last 4 BIOS releases, taken from on the ASUS downloads page. I see nothing about 1107.
Z9PE-D8 WS Formal BIOS 3206
release (2012.11.07 update)
1. Fixed BIOS System Event Log record with error Date.
2. Adjust Ai Overclock Tuner to support manual mode.
3. Support Manual Mode on each PWM of fan.
* Pls noted if MB BIOS version is older than 3109, users need to flash to version 3109 (rom file) firstly before updating to version 3206 (cap file).
Z9PE-D8 WS Formal BIOS 3109
release (2012.09.27 update)
1. Support Windows 8 OS.
2. Fixed UEFI OS installation fails.
3. Fix system may hang if NVRAM corrupt.
Z9PE-D8 WS Formal BIOS 0703
release (2012.08.22 update)
1. Fixed onboard VGA always be disabled when addon VGA card exist.
2. Fixed PCI out of resource issue when all PCI-E slots plug-in all VGA cards.
Z9PE-D8 WS Formal BIOS 0503
release (2012.05.17 update)
1. Support LSI Mega RAID Function.
2. Add memory ECC enabled/disabled info in BIOS.
3. Update Intel RSTe 220.127.116.115 Option ROM for SATA & SCU.