I think it'd be useful to benchmark GWT-generated JS (and also Objective-J), but not Scheme2Js, which is rarely if ever used in practice. Compilers for different languages will emit code with completely different performance characteristics and feature usage patterns. (For instance, Objective-J particularly stresses the call site caching mechanisms in modern JavaScript engines with its "objc_msgSend" equivalent, since the indirect call in that function branches to so many different call sites.)