GPU Upgrade necessary for 2nd/3rd Monitor?

[elvee]

With the new iMac (27") is a GPU upgrade necessary to drive one or two more monitors connected via Thunderbolt?

Not going to be doing any gaming but occasional video and graphics.

 

[Intell]

No, the current and previous iMac were able to do it well with a less powerful GPU. Even the retina Macbook Pro running on the Intell HD 4000 could drive four display, one of which being the retina display, without problems.