I've gone down to Vil quite a few times and for me, it's a 700km journey, through the park, crossing at Pafuri gate and then to Vil. It takes a day and a half. Firstly, you are supposed to stop over because of the park rules, but this can be dodged. We have taken to sleeping at Mapai in the Parc Nacional because it breaks the journey nicely. The tough bit is from Pafuri down to Mapai. It's very slow going depending on when the last rain fell. From Mapai to EN1 it's dirt road that varies between good (comfortable 80km/h) to a bit dodgy (40km/h). Then tar when you hit EN1 up to Vil. I will always take this road provided it's been reasonably dry in the run up to my trip. Which ever way I go, it's more than a day's trip. Through Pafuri, it's a short trip in km and very cost effective in diesel.
I have taken my various boats through Giriyondo post. That's a lot of dirt road but reasonably reliable and moderately well kept.