Hey Matt,
I have what is commonly referred to as an Extreme Giant tegu. They really are nothing more than a "whiter" Argentine black and white tegu.
Tegus CAN get 5+ but I don't think it is too common. They more commonly reach 4+ and 15lbs. I really enjoy mine. He is very personable and almost enjoys coming out and cruising around my herp room when I'm cleaning other enclosures. He will explore every inch of the room and end up right between my legs (in the way usually).
Mine is hibernating right now which is good and bad. Good because I don't have to feed or clean, just provide clean water. Bad because I don't get to do anything with him which is what's fun about owning tegus.
I received mine from Johnny LaRocca (teguterrra) and wouldn't hesitate to recommend him to anyone else. He's an all around good guy.
If I had a whole room to dedicate to a large lizard, I would likely have a trio of tegus over a large monitor but that's just me.
If you really have your heart set on a HUGE lizard, then a tegu probably isn't what you're looking for. They get plenty big but they are far from HUGE. You might try finding someone local to you that has one and see what you think. I've had monitors and they were all OK but my tegu has never bitten or tail whipped at all. A little hiss occasionally but only if I startle him. If you start with a hatchling they take time to calm down but mine was about 2' when i got him and already pretty calm. It took about a week to get him to relax completely with me.
This is what I bought, hope this helps...
http://www.teguterra.com/apps/websto...s/show/3239560
Josh