Much good sense there but I'll add just one point about getting your money's worth for all those pixels. If you want to enlarge a small part of a large picture then you can do so without your masterpiece turning into a modern art creation made from little rectangles.
Now, a serious Query, PPT. I have amost decide to go to Mac just to stop PhotoShop turning to glue. Aren't you a Mac person? Does it still grind to a halt with large file sizes. I can do a 50MB file even on a PC. Would a Mac cope? Help, my credit card is poised.