I think by turning off reduced transparency you'll have much improved performance across the board. I do believe my 1.1 ghz doesn't lag when opening new tabs with it turned off.
How long does it lag for? Mine takes about .2 seconds I guess...not quite as fast as my MBPr, but I wouldn't expect it to be.
**I also noticed that cmd+t doesn't lag at all...
well it kinda helps. anymore workarounds?
yup latest osx.Are you running OS X 10.11.1 El Capitan?