All signs are pointing to 60'. The R32s are showing their age, and they need to go, but not as urgently as the R42s.
The R46s aren't going to be replaced by the R179s, the R46s will be here until at least 2015, and will be ousted by the R211s. The R179 was originally intended to replace the R44s (and thus were designed to be 75 footers), but the R44s had to go badly and now we're here.