The K-1 has the 105mm. The K1A1 has a 120mm.
Do not get confused. They are quite different.
Plus I think we've stepped into the territory where the terrain and situation just count because both tanks have their strengths and weaknesses. I think because the Challenger is so heavy, it'd be quite crap in Korea with all the hills.
The Challenger's gun has a better range of 3000m ahead of K-1A1's 2000m. Might be 2500m but I am not entirely sure of that.
Also the Challenger probably has superior armor.
Speed seems to be the same though. Roughly 55km/h.
The K1A1's armor is probably the same as the M-1A2.
So in a flat terrain, the Challenger II is flat out better. But I think with the K-1A1, they had bad terrain and closer ranged engagements in mind with all the hills that Korea has. Chances are having an open shot for 3000 meters won't come very often. Faster and more accurate target aquisition is more important.
I'd say 50/50.
The main difference between the K-1A1 and the M-1A2 is that the K-1A1's engine and performance was based on non-flat terrain while the M-1A1 had flat terrains in mind. By dumping the gas turbine engine for the diesel engine, the price also dropped considerably as well as fuel economy.
A link about the K-1A1
http://www.globalsecurity.org/military/world/rok/k1a1.htm
And a post from someone about how Australia might buy the K-1A1 instead of the M1A2
http://strategypage.com/messageboards/messages/2-6782.asp
