Got it! that admin menu really made me think something's wrong with speed, anyway, many thanks for clarification, just planning to shift to Moodle 2.6 now , good thing everything came on the right time for me else I would have been re-doing lots of fontawesome 4.0 code .
Slight visual issues in Essential for 2.6, though one is already addressed above and I have just downloaded the latest master from github, still same output
As long as 3 icons are there, they align properly, anything more than 3, the last one mis-aligns with others.
same case in IE-10 and FireFox (latest) - as shown above, deviance is slightly lower than others, in Chrome however its marginally up.
also (I wonder is others havent noticed, or is it me only having this issue, but had been tested on 3 different platforms and 7 different browser versions)