I have that Sigma lens and I enjoy it very much. I found that the Canon 50mm I had was forcing me to stand too far back for indoor shooting. The Sigma 30mm fixed that, and the image quality is great. The DOF can get quite narrow, but if you've been using a 1.2, I'm sure you're prepared to handle that.
Maybe you could keep the 1.2 and buy a 35mm f2,0 to complement it. I have one and it is a quite good lens and one of the least expensive in the Canon range.
What you propose is, I think, a very viable strategy. The 35/1.4 will give you a very fast lens of stellar quality that will act very similarly to a 50mm lens on a 35mm frame; well, actually more like 56mm, but who's counting?
The 50/1.4 may not be an L, but is still a fast, high-quality 50mm prime with great bokeh. The one minor irritant with the 50/1.4 is the extending front element (but not rotating, and that is important).
Let me tell you there is something magical about the 35Mm F1.4 lens. I had it and just plain loved it. I never could get that feel from the any of canon's 50MM lenses. I had several 50MM F1.4's and had one 50MM F1.2, on a full frame camera the 50MM F1.2 was OK for focal length but there really is something dreamy about the 35L. on the 1.6 crop you might consider a 24LII instead. Better focal length for that camera and "almost" as good as the 35L.
Hey guys thanks for all the input. After much deliberation I have decided to keep the 50mm 1.2 and for a third of the price of the 35L get a Sigma 30mm 1.4. After shooting with 50mm 1.2 I just really did not want to get rid of it, its a really great lens. Considering the price, the difference between the Sig 30mm and the Canon 35L is very minimal.
