Okay so i finally sold my big lens (tamron 200-500) and i'm considering reinvesting the $ into some glass that will get a bit more use. Right now i have a tamron 17-50 f2.8 that i use a lot and i'm looking at picking up a used canon 28-70 f2.8 L or something similar. . .i like the 17-50 range but i would like a little more reach on the long end, and i would like to take the plunge into L glass. . .the other option would be a 70-200 f4 non IS, as i've heard a lot of good things about it. Any thoughts?