15 or 17 inch MacBook pro?

I need something to type, and teach classes as a high school student teaching programming. I will also be using it to teach a 3d design and compositing class (yes, my school need funding :) ) I want a mobile workstation. I was leaning towards the 15 inch but it just doesn't have a high enough resolution. Now I want the 17 inch, but how much bulkier would it be? Would it fit on my lap comfortably? Would it be considerably hotter? This would be my first Mac and I need power. It would be specced to about the $4000 ish price range.