My understanding is that the life size converter doesn't change the focus distance of the 50/2.5 macro. Without the converter the focus range is 0.75ft (9") to infinity. With the converter the focus range is 0.75ft (9")to 1.4ft. Thos measurements are subject to film plane (sensor plane) though, so I guess the front element of the lens+converter ends up being closer to the subject by the length of the converter, so the working distance is reduced. My understanding is that with the life size converter attached, what you have is essentially a 70mm macro lens.
The focus range of the EF-S 60/2.8 is 0.66ft (8") to infinity, so it's still going to be pretty close to the subject at high magnification. I think the actual working distance at 1:1 is around 3.5".
The only way you can maintain magnification and get more working distance is to go to a longer focal length. The longer the better, so if you needed a true macro lens, you'd be looking at the Canon 180 macro
(not cheap at close to $1600). That gives you about 10" between the subject and the front of the lens at 1:1 magnification.
The 100mm macro lens has a working distance of around 6" at 1:1 magnification (subject to front element), so that's still tight.
An alternative is to use a high quality 2 element closeup diopter lens on a telephoto lens. Something like a Canon 500D
on a lens like the EF 70-300/4-5.6 IS USM
. It would give you a working distance (subject to front of lens) of around 18" and a maximum magnification of around maybe 0.7x?
There's more info here - http://www.bobatkins.com/photography/eosfaq/closeup2.htm
The bottom line is that the EF-S 60 macro will give you higher magnification, but it won't give you significantly more working distance than the 50 macro, or at least not enough working distance if you need to go to 1:1 and can't get closer than 12" to your subject.