I agree with pretty much everything said in the responses thus far but I have a slightly different take on it.
I have a thrust stand and a watt meter and various batteries and motors and props (when you do this for a while you will end up with a collection) and so I can pick and choose what I might consider an optimum setup for a plane and my experience with these components informs any further buying decisions I might make.
But when I started - no motor, no prop, no ESC, no battery and little knowledge - and wanted to come up with the best possible option for a power setup for the least number of dollars, I trawled through the internet. One post I saw on RC groups basically said "find out what other people are using and start there". "No way" I thought. I was going to do the research and math and more research and get the best possible option. After hours comparing setups using online tools, comparing prices online, and reading about how all this works, I eventually settled upon an NTM 2826 1200kV motor, 3S battery, 25A ESC and 9x6 and 10x4.7 props. And you know what? This was basically the original C-pack power configuration that FT used. I could have saved myself a lot of effort by simply going with "what other people are using".
It's good to do the research and learn and gain the experience but you can't test components with watt meters and thrust stands unless you have already bought them. So I would start with what is a good recommended setup to get into the air. For the Viggen, get the C-pack motor (either the Emax or FT radial version) , an 1800 - 2200mAh 3 cell, A 30A ESC (4S capable) and some 9x4.5 SF props. This will get you into the air and give you plenty of punch-out (quick response). Then you can start to expand your collection of props (9x6 APC, 10x6 APC) and see how you like the additional speed (with some sacrifice in punch out) or invest in some 4S batteries and satisfy your need for speed (if you have one). This motor / ESC / prop combo will pretty much cover you for any 25-40inch wingspan weighing up to 2.5 pounds.
If you want to see some of the performance data for the FT Radial C-pack
I have posted my test results here. (although it would be nice for FT to start running and publishing their own data as suggested by
@kdobson83