I considered buying the lens some time ago, but the thorough technical reviews made me realize I didn't want what the lens had to offer. I think you'd do well to spend the $1200 price difference on some more-valuable equipment
Canon EF 50mm f/1.2 USM L (full format) - Review / Test Report
"Vignetting:Vignetting is a delicate topic for ultra-large aperture lenses used on full format DSLRs and, yes, the EF 50mm f/1.2 USM L has its share of problems here as well. At f/1.2 we're talking about more than 2.7EV - this is extreme and somewhat disappointing regarding the very large diameter of the front element. The situation does only marginally improve when stopping down to f/1.6 and it requires f/2 in order to reach acceptable levels here."
"MTF (resolution): Technically the EF 50mm f/1.2 USM L is a mediocre performer with respect to its resolution characteristic. The center resolution is quite fine even at f/1.2 but the border quality is very poor till at least f/2. At f/2.8 the center quality is boosted to excellent levels whereas the border quality remains fairly low and you need to stop down to f/4 in order to achieve good quality results here. The peak performance is reached at f/5.6."
"All-in-all one of the weaker MTF curves that we've seen here. To be fair - the lens is simply designed to produce usable results at ultra large apertures and in this focal length class this is obviously only possible by compromising the peak performance. If you do not believe our findings here feel free to check the original Canon MTFs for this lens - they suggest a similar characteristic here."
"Lateral Chromatic Aberrations (CAs): The EF 50mm f/1.2 USM L is quite prone to lateral chromatic aberrations (color shadows at harsh contrast transitions) - an average CA pixel width around 2px is unusually high for a prime lens."
"Verdict:SNIP> However, when looking at the whole image frame the results are generally less than thrilling. The border resolution as well as the vignetting is rather poor from f/1.2 till f/2. The situation isn't all that bad at f/4 and beyond but if you're looking for superior -technical- quality levels this is simply not the place to be. The level of distortions and lateral CAs is also not overly impressive for a prime lens. It is tricky to judge the quality of the bokeh. The lens is surely capable of producing an exceptional "cream" at very large apertures - more so than most lenses thanks to f/1.2 of course - and the bokeh is also technically perfect near in center of the image field. However, in critical situations the border and corner bokeh can be very nervous. It's not a show-stopper but you've to know what you're doing here (keeping a pronounced focus spread between your main subjects and border structures). The build quality is fantastic and it's a joy to play with the lens out there but at the end of the day its the image quality that counts and there're some question marks where the global performance is in line to the rather hefty price tag."
Sooooo, please note that in the review, the reviewer wrote; "The result of this review will probably cause some "friction" in the community. Canon L lenses are some sort of holy grail and criticizing such lenses is usually not overly well perceived." So, be prepared for fans of the lens to come to its defense. Those who love to put a little red "L" after every lens listed in their profile often own this lens, which does have a high status among Canon users.
