I think Sigma was selling refurb s35s for something like $640... I'd jump all over that if I were you.
s50 will be most like your s30 was on crop, a replacement for 100/2 would be 160mm, so the closest you'd get to that would be a 135L since you already have 200mm. The 85 would be like a 50mm was on your crop body.
I do love my s85 1.4 though.
$640, wow. I would probably buy one now if they are still that cheap.
I do enjoy my S30 on crop, and it seems the S50 is real similar in IQ and sharpness. I used a 50 1.8 for months before caving for the S30--was too long for indoor candids and the AF too sporadic.
I do wish I had something a bit wider on occasion having two kids under two and it seems the S 35 has some of the best IQ for under $1000.
The 100/2 is pretty long on my 60D but I do my best to make it work because it is so sharp and it focuses so fast. More of the same with the 200 2.8, but the colors are better to much better. I'll miss the crop factor for field sports but little else. On those occasions there is a T4i that I can borrow as a second body.