If you clean your history well, I've been up to ~4-4.5 million triangles on this Core2Duo E6600 + GeForce 7900GT; it was sluggish but it worked. It was smooth at 3-3.5 million

That being said -- a bunch was redundant so Maya may have instanced some things in the videocard. (Note: They were NOT instance objects... but you never know how Maya might try to save itself some performance. Also note: They were solid-shaded)