I just benchmarked an iPad 2 as around 4.5X slower than an MBA 11 1.6 GHz at general integer computing, but only around 2.5X slower at some floating-point number crunching. The MBA 11 is about 1.75X heavier, so it wins in CPU performance-to-weight ratio. But not by that much over something not even being advertised as a fairly powerful number-crunching computer. The iPad 2 also benchmarked between 1.4X and 2X faster than a 1st gen iPad. The benchmarks I ran were in fairly generic single-threaded portable C code compiled with full optimizations using Xcode.