SunSpider JavaScript Benchmark marks 37% faster score on iPad 2 / iOS 4.3.1 / Mobile Safari 5.0 compared to iPad 1st gen.
Also note that iPad 1 could get significant peformance improvement by updating iOS from 4.2.1 to 4.3.1. This means Mobile Safari 5.0's "Nitro" Engine enabled on iOS 4.3 runs JavaScript quite fast.
Benchmark results captured are below:
iPad 2 - 4.3.1 and 4.3
iPad 1 - 4.3.1 and 4.2.1
PS.
My Mac results 344ms on Chrome and 360ms on Safari.
iPads are still nothing compared to Mac. :-<
* Japanese version of this post is here.