There is another factor to consider
yes the F1.4 is a full stop on from the F1.8 which means it will let twice the amount of light in, however it also means it will make the already bonkers shallow depth of field even shallower, a portrait at F14 would have the eyes in focus and nothing else, the nose would be blured on a human let along a dog
to get the right depth of field and the right light, I end up often shooting at F4 or F8 but then with good light or a flash
I have a Canon 430exII flash and a cheap set of ebay radio triggers so I can use it off the camera ... now thats an investment that has changed a lot and allowed me to do SOOO much more
just some more info for thought
oh ... go into a shop, try both, take a picture of an a4 sheet of text at 45 degrees to it so you can see the depth of field, and then think when will I want it so shallow ?
Phil