Not just the javascript either, Chrome becomes horrendously slow with week wifi signals where Safari is fine. For some reason only Apple apps can do the 3G/LTE/Wifi request pooling magic that they added in iOS 6.
Unusable?! I've been using Chrome on my iPhone 4 for the past week and I haven't noticed a significant difference.
jailbreak + nitrous. problem solved. :)
Did that for a few weeks, and the Chrome performance boost was nice. I had to jail-unbreak though because stability was horrid for me, with applications constantly crashing :/