My BIOS philosophy is, if it isn't broken, try to break it with the newest version...
Seriously, I don't own your specific board, but do use a very similar board, ASR Z77 Ex 4. I've update the BIOS/UEFI ten times on my board (many new versions, not because they were buggy) using Instant Flash, and have never had the slightest problem.
The added PCIe speed settings and detection was added in a UEFI update to my board too, and they work fine, nothing to fear IMO. A 600 series video card I use will cut the link speed to PCIe 1.0 when just using the Internet/low stress, so don't get worried if you see that at times. If it does that during gaming, then the video card likely has problems.
For me, the updates for Windows 8 that are also listed for your board (doesn't seem to be all of them) were important, as I use Windows 8 (or do you hate-8?) I installed Win 8 for UEFI booting and it all works perfectly, I'm even able to use a video card whose VBIOS had an update to support UEFI booting (GOP support.) Otherwise you're stuck with the on-CPU graphics, which are Ok.
I have not seen any complaints about the new UEFI versions for your board, or really any complaints about it that I can recall, so you should be fine.