OK since it looks like everyone missed a key part of the question...
Aluminium radiators are typically 1" thick cores
Copper radiators are typically 5/8" thick cores
So a 2 core aluminum has 2" of core and
3 core of copper has 15/8" (that's 1-7/8" of core thickness)
That puts the thickness meter at about a wash. Get even more technical and remove the leading and trailing edges and the 5/8" copper cores only have about 1/2" of contact with the fins. Then there is find design, fin count, and a tone of other little variables.
So a 2 row aluminium is about the same cooling as a 3 row copper, or maybe 4 rows, or maybe a little less...
With a good fan, a properly functioning shroud, either should do a decent job cooling your engine. Installed poorly, neither will do a good job.
Then we can jump all over the copper/aluminium debate as far as heat transfer rates, what solder does to those in copper radiators, fin count, multi pass, repairability, etc.