I have roughly 1200 CAD to purchase some lenses for my 600D

Hello DPreview!

This is my first post on this forum, so yea...

Anyway, I have roughly 1200 CAD/CDN to purchase some lenses on my 600D. I plan to stick to APS-C sensor bodies for a long time, since I'm not really impressed with the 6D, and the 5D mark III is $3500, which is just too much money.

I currently only have an 18-55 kit lens. I did have a 24-105, but I returned it, thinking I could have a better setup in terms or optics and IQ. Also, the 24-105 range didn't really make sense on a crop senor. I'm thinking on the 17-50mm Sigma and the 50-150mm Sigma F/2.8 EX DC OS HSM APO. I would get one more stop of light and still have OS.

Any suggestions?