I double checked it, I think the speed was wrong for a while in that AC and it's more correct now. It'll still easily get up to and exceed mach at tree top level but you're looking at a top speed of about 1.7.
There's absolutely NO way that the Viggen or any other manned fighter aircraft for that matter is able to reach Mach 1.7 at low 'tree top' altitude (or sea level) let alone Mach 2!
Below someone did a study and concluded that the Viggen's top speed at sea level altitude was Mach 1.1 and this in an almost clean configuration (with only 4 AAM's):
http://www.temporal.com.au/viggen_final.pdf