Well I think you're going to find the Fusion just a bit more than the 788. However, that said, if you really are going to use this for film, you're going to want to enter STN information. On the fusion this can be done via the touch screen. On the 788, you have to use a USB keyboard to do it. The 788 isn't the easiest thing to mix with, so you're going to need to use an external mixing board with it, on the fusion, you have all channels available for mixing from the unit itself.
As far as the Nagra goes, I do hope they can really make a go at the digital realm this time. They have tried and tried, but just haven't been able to really break out with a product. The new Nagra from what I can tell is around 5,000 euros, haven't been able to find a US price, but that would put this unit in direct competition with the Fusion. It does have some very nice features on it, but like many recorders is limited by hardware. If they want to add a new feature, they will have to make a new box and a new knob. One of the best investments I have ever made was getting the Deva three (nearly four now) years ago. The unit is nothing like it was four years ago. Substantial changes have been made via firmware updates, from on-screen faders to routing options, eq, compression and more. The reason this can be done on the Deva and Fusion is because while the box itself looks pretty utilitarian, the color touch screen allows Zaxcom to continually update and modify the unit. If they need a new feature, they simply add a new button or screen to allow that feature.
Again, I'm very biased, and while I see nice options from other companies, I still haven't seen any recorder that has as much flexibility and versatility as the Zaxcom Deva and Fusion for film work. But then, I work on productions know the stress mixers and boom ops are under when filming, and what is required on set.
Wayne