I don't know the viper but I started on a funster 165l board. I am 6 foot 1 and weigh about 95kg. Having the slightly smaller board meant that I had plenty of float to uphaul etc. But that I could progress with the board to intermediate without having to change boards.
195l would make it easier at the beginning but once you pick it up, you may have to change to a smaller board sooner which equals dollars.
When beginning I would tend to look at something with a bit of width as this will give you stability.
Best bet is to go and see pete at on onboard as he can tell you what size you would need and they sometimes have second hand gear they can match you up with.
Pete matched me up with the funster board and the 2 Maui sails I have for sale at the moment and it allowed me to progress quickly with the right setup.
