Hello Tom!
First of all, let me say that not much good usually comes out of such hypothetical questions!

One thing that you must consider is that there are SO MANY factors that can effect such an encounter. Also, and given fighter can lose on any given day, regardless of their previous training or fight history!
The art does not make the person, the person makes the art! A really good Wing Chun man could probably destroy a fair to medium skilled boxer. A really good boxer could probably take out a fair to medium skilled Wing Chun man! Now, if two highly skilled experts in each were to fight with NO RULES, I would have to go with the Wing Chun man. If they fought under boxing rules, I think the boxer would have the advantage. Then there are all potential variables that could effect the fight to consider, which there are far too many to discuss here!
That may not be the exact answer that you wanted, but at least it is an honest answer based on the question asked! Time to go do some work at my kwoon now! Have a great remainder of the day!

Keep Blasting!
Sifu Lamar M. Davis II
Senior Instructor
Hardcore Jeet Kune Do
Sifu@HardcoreJKD.com
JKD@windstream.net
http://www.HardcoreJKD.com
Phone (205) 296-7070 (Incoming Only)
"Hit Hard, Hit Fast, Hit First - ALWAYS!"
"The REAL future of Jeet Kune Do belongs to US, the few, the proud, the HARDCORE! Now, what are we going to do with it?" _ Sifu Lamar M. Davis II