GIMP I find to be pretty cool. It's not as extensive as photoshop is, but it actually works better on my toaster of a chromebook (Yes I use a chromebook, but I have debian installed on it), so I might often use GIMP instead of krita for digital painting if I'm using a low spec machine because GIMP I find takes up less resources than krita does. I don't wish to compare the two together, I just like GIMP as well. Krita is still a very good program. It depends on what you want to do with it. Krita has more blending options so if you want some specific art look, krita might be more suitable.
Guidodinho
I also have a spare toaster, but with a Linux Mint on it. And also found that Krita was quite good on it, but used quite a bit lf recourses on my lil toaster. But an old version of photoshop(CS2) ran a lot smoother than krita did. A little glitchy because it ran through wine, but nothing breaking much functionality. Only a bummer that the pen tablet pressure doesn't seem to work with windows applications running through Wine.
Other than that, a dusty old version of PS oughta work quite decent on a crummy old toaster.