need to know the resolution of the image. to know what it can realistically handle in a real world situation. remember if someone like a photographer is using it, then they are most likely going to be loading 16-30 megapixel images.
PS these onboard GPU's are just as fast as some of the videoocards that people were happy with a few years ago with photoshop so there is no doubt that it handles photoshop really well. The only issue is can it handle a modern workload involving many high resolution images.