Get the 50 1.4. Then you can save up for the 40 and buy it yourself - it's cheaper than the 50 so you'll get there more quickly.
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That leaves a 17-55 vs Sigma 30 1.4 debate. On image quality alone would the 17-55 maybe be preferred in most cases? I'm getting good with my flash and don't really need less than 2.8 for non-indoor sports pics.
it would only be a problem with the current EF-S 10-22 since that is the ONLY EF-S lens that takes some advantage of the EF-S short back flange concept (rear element closer to sensor). All other current EF-S lenses have no rear elements protruding into the mirrorbox.
The main reason that a larger sensor means shallower DoF is that for the same framing with a smaller sensor, you need to either be further from the subject, or use a longer focal length, either of which means deeper DoF.