From my point of view the galatic empire would win.
I like to point out to ww2.
Japan was by very definition stronger then the usa.
Yet the usa won because of there industeral might.
Even(and i highly doubt it) if the sith empire was able to win every fight agains the galatic empire they would still not be able to replace there losses as quik and the galatice empire could.
I respect your opinion, but this example isn't the best - seeings as Japan did not have force users
If anything it works the other way. Japan is stronger than the USA (I don't know if thats fact but I'll take your word for it) much like the GE is statistically stronger than the SE. However the USA had nuclear bombs, which they dropped on Nagazaki and Hiroshima (which was disgusting by the way, just saying) and ended the war. These nuclear bombs represent the Force and its tremendous power. So the force users of the SE are going to be like dropping bombs on Japan. But thats just how I see it.