The right size for programming is a desktop with at least 2 monitors and a full, proper keyboard. Laptops make no sense if they are big. Programming, gaming, and working on a laptop is inferior experience in any way imaginable. What you get in return is mobility. To sacrfice mobility with 17"-er is not something I'd recommend. For gaming, many university dorms offer common rooms with huge TVs, or if you've got 24-hour access, you can hook your console to the lecture projectors (do try and watch movies in the lecture halls... it's a lot of fun !)
It all comes down to preferences in the end.
It is true that with multiple monitors you can increase your efficiency even more - and you can do it as well with a laptop. The 17" I've posted above has a full keyboard as well. This is probably not the best choice in terms of mobility but rather a desktop replacement, which as I've read is what we're looking for (as the larger size issue doesn't matter).