I am still trading emails with Gigabyte and their last one is a real eye opener.
First the backstory. I got the UD3 up to 4.52 ghz but could go no further because that was its thermal limit. Then it overheated and warped anyway, so it got RMA'd. Currently I'm using an MSI 990FXA-GD80 that is running cool at 4.6 ghz. The new CPU cooler and some better case fans arrived last night, so 4.7-4.8 ghz is coming soon.
Anyway, here is Gigabyte's last reply in full.
We don't believe replacing the motherboard with a REV 4.0 or UD5 will solve your issues. These motherboards are design the same way and you may still experience the same issues due to over clocking and aftermarket heat sink.
Make your own decisions.