The CPUs were just not capable of doing much more than 170MHz BCLK. To fully use the 2.5x ratio, you'd need to use a BCLK of 68MHz with 2.5x gear ratio. Anything below 95MHz BCLK on SB-E was already a struggle.
Hm, seems like support for E1/L1 requires a microcode update. I'll check with MSI HQ tomorrow morning. The latest beta BIOS is H74, but I doubt that one works as it's from somewhere in april.
http://www.filedropper.com/e7751ims
T-branch was Intel design, but ASUS was the only ones doing optimisations to that design, no? At least, that's what I gathered from all the forums posts.