Dam#!! You are making me want to send back my f/1.8 when it gets here.
You may not see much difference right now between the f/1.8 and f/1.4 as far as the image quality goes. In fact, you may not notice much in the future. But in certain conditions, you will see them. Especially when you stop down the lens a little bit. (i.e. f/2 -F/4), you may see the pentagon shaped bokeh mainly due to number of aperture blades is 5. (vs 8 in the 50mm f/1.4). Here is a photo I took that show the iris of the lens.
The on the left is f/1.4 while the one on the right is the f/1.8 version 1. They were set at f/4
Since the f/1.4 has more blades, so the iris appear to be more circular than the f/1.8 version. (I or II)
But as I said, I do not think you will see the differences in terms of optical quality right now. By the time you do and like to get the f/1.4 or other better lens, you can always sell it back. (Just don't break it)
The 50mm f/1.8 lens is a popular lens so I do not think you will lose much when you sell it. 3 years ago, the EF lens sold around $89 new at
Adorama. And now, I saw people list it on craigslist around $8x used.