PP, it is a bit confusing but my understanding is that people are thinking multi-frequency across Park, Field, Beach and Gold Modes are exactly the same - but they are not. Different modes are 'weighted' towards different frequencies and the 'type' of different targets you are likely to come across in the 4 different locations.
If they were 'exactly' the same then there would be no need for the 4 different modes. Again, the Multi IG treasure talk number 3 discusses these weightings and I think it is the second link I have put above shows all 4 Multi IQ blogs.
But, as the picture that Hayyou has shown further up this page the Multi IQ spread IS right across the full 5 Khz range - it is only the single frequencies of 20 and 40 khz that are singularly selectable on the 800.
Plus there are the different back light options, audio options and recovery speed options making the 800 more adaptable.