Focusing screens for cameras with autofocus tend to be - almost per definition - optimized for use with autofocus lenses, which tend to be relatively "slow" with an aperture in the f/3.5-5.6 range. In olden days, focusing screens were optimized for fast, manual-focus screens, but those screens had the downside that they grew unusably dark when used with such slow autofocus lenses. The price paid for the extra brightness of the modern screens is a decrease in focusing accuracy; it is accurate enough for this kind of AF lens but does not show sufficiently accurate focus information for lenses much faster than f/2.8... the reason being that there are microprisms in the screen itself that impose a certain minimum depth of field to the image. Think of it as the focusing screen being an f/2.8 lens looking at the image from your f/1.2 lens, what you see in the viewfinder will be at least f/2.8 no matter what.
This is a bit of a dilemma - you can't really have your cake and eat it too. Your focusing screen can either be accurate but dark, or bright but inaccurate.
While Canon do not find it worth their while to offer superfast focusing screens for fast lenses (with the exception of some of their top-end camera models) third-party suppliers such as Katz Eye Optics do. What they do is basically to take a good old-fashioned manual-focus focusing screen and file off the edges (quite literally so in some cases, at least that is how it used to be) so that it fits into your modern camera. These screens can be of the classic coarse-grained type, which give a good "focus pop" on fast lenses, or they can be of the kind that have a split-prism in the center of the image. In either case, they will be very good for manual focusing of fast lenses and possibly utterly useless with slow autofocus lenses! In other words, you will want to swap focusing screens when swapping between slow and fast lenses.
I am not sure if the Canon 60D is designed for user-replaceable focus screens, if it is not then swapping out the screen can be a bit fiddly and probably something you would want to do at the kitchen table and not out in the field. Even if it is designed for replaceable screens replacing one can still be a bit fiddly so be warned :)
Of course, the camera's light meter meters the light AFTER it has passed through the focusing screen. In other words, replacing the screen affects metering, possibly in a non-linear way. This is an added complication when using third-party screens, you will want to meter the light with a separate light-meter as the camera can no longer be trusted - and you will have to use the camera in M mode instead of any of the automatic-exposure modes. Effectively, you will have entered a photographic timewarp and will have to work like they did in the early seventies.
Note that even if you use an official Canon screen other than the standard one you will have to go into the camera's menu system and tell it exactly which screen you are using, the camera will then know how to compensate the light metering accordingly.
