I've definitely observed this performance difference, and it is quite significant. However, the new AES-NI instructions in more recent Intel chips may lessen the performance difference over time, as more users buy machines with these chips. (Of course, that won't help mobile devices yet, and it's possible that one could equivalently speed up RC4 with those instructions as well.)

But I know the latest OpenSSL does have an AES implementation that uses AES-NI when those instructions are supported.