I have both the 100-300 APO D and the 100-400 APO, both of which I use on an a700. Both are older lens designs that lack digital coatings, and the filter rotates on both lenses while focusing, making it more difficult to use CPL filters.
I agree with everything Mugen said about the 100-400 APO. One positive feature is its size and hand-holdability. A negative is the lack of a tripod mount on the lens. Unless you can get one at a bargain price, I would not recommend it for use on your a850.
The 100-300 APO D is a pretty good lens that is a very convenient size for travel. Not sure how well it performs on a 24MP camera, however.
Undoubtably, both the 70-300G and 70-400G lenses would deliver better image quality on your a850, although larger and more expensive than the 100-300 APO and 100-400 APO, respectively. From what I have read, images taken with the 70-300G and cropped to 400mm are at least as good as those taken with the 100-400 APO. If you want a one lens solution, the 70-400G is undoubtably the best of the bunch, although heavy and expensive, while the 70-300G would most likely outperform either the 100-300 APO D or the 100-400 APO (except for the more convenient size of the 100-300 APO).