I would really like to get the 4K 21" iMac (the 27-inch is just so BIG and I'm going to college next year and not sure how much room I'm going to have). But the fact that it doesn't allow a dedicated graphics card seems disappointing. But how much of a difference does it really make? I'm not a gamer, but I do use Photoshop and Lightroom regularly and it seems like a 4K screen might need something a bit more powerful than Intel's integrated graphics. Is there any kind of "sluggishness" in comparison with the 27-inch iMac or is the difference negligible for most things?