eSprit65 has so much going for it above other backs with the one downside being the crop factor, in my opinion, which is the same as a P30 for example (44x33mm). If that doesn't bother you then you should definitely take a closer look at that back. The eMotion75LV is the main competition. It lacks some of the eSprit's advantages but it has a 48x36mm 33MP sensor and the latest version has really decent high ISO performance. Many downside of this back - the slightly slowish frame rate. Both of these backs should work with Sinar's rotating adapter, afaik, which is a real plus. There are other Sinar backs which are for tethered use only and include features such as multishot but I assume these are not so interesting to you.