If Reed  decided to turn evil and focus all his abilties and knowledge into aquireing the infinity gauntlet and a cosmic cube, then spending 6 months learning about and mastering them both what would be the lowest level person able to beat him?
 

• Bare in mind i mean a completly evil Reed , so no Sue or children turning him back to the side of good
  

Sounds like you just want Reed to destroy the universe :P

lol @ Namor carrying Professor X who looks like a baby.

Heroic Victor Von Doom

Evil Reed didn't stand a chance against the combined might of Valeria Richards & X-Factor.

 The only reason Reed's still alive is that Doom's not allowed to kill him because in the end, the good guy has to win.  If Reed is the bad guy, he loses badly. 
 
Consider 
 Reed + Johnny+ Sue+Ben is slightly better than Doom alone.   
 
Therefore: 
 Reed alone< Doom alone    

Doom, Pym, Banner and Stark would find some way to take him down. Granted, it may take years and cost billions of people their lives, but they would eventually get him. 
 
Good thread :)

Ive always thought Doom could take down Richards if he really wanted to but just chooses not to for sport.

The combination of Hulk, Galactus and Dr. Doom.....maybe. Pure strength, big alien who eats worlds and science/magic.