There's nothing wrong with the 5DII's autofocus system for landscape or most any other kind of "sedate" photography. It's just not the quickest or best tracking for moving subjects, so not really ideal as a "sports" camera (though it can be used for that, you'd just have more missed focus shots). 50D's AF system is better for sports/action (so is 60D's, and of course 7D's). The current Rebel/xxxD series have AF most similar to 5D series'.
I'm also not buying some of the "leaked specs" of the highly anticipated 5DIII. Canon might surprise me, but I really don't believe that 5D Mark III will get the same AF system at the 1DX. I'd think it a lot more likely to get something similar to the 7D's (which still would be a very nice upgrade). Think about it... Why would Canon make a $3500 camera so comparable & competitive with their still unreleased top-of-the-line model that sells for twice as much. I also don't believe the dual memory slot spec: one CF and one SD. Canon has just - finally - gotten away from mixing memory types. The 1DX will have two CF slots. It's been a bone of contention and some complaints for years, that Canon has insisted on mixing CF and SD in their 1D line, and they finally have stopped doing that. Why would they reverse that in 5DIII? (It's also kind of funny that Nikon, which for years has put two CF in their high end cameras, has just announced the D800 will have a mix of CF and SD. D'oh!)
I prefer to use 5DII for landscapes, mainly because landscape shots often lend themselves to big prints... really big prints. But to be honest, 50D or one of the newer 18MP models can do pretty darned well.... I've posted these images before so please excuse the repetition, but it can be pretty hard to tell apart a 50D image from the 5DII image, at least as large as I've printed them to date (12"x18" or 12"x16"):

Pigeon Point LighthouseDetail from aboveMorro Bay HarborDetail from aboveBoth the above were shot with the same lens (EF 20mm f2.8) and even the same filter (B+W Kaesemann C-Pol). One was shot with 5DII, the other with 50D. Frankly, when post-processing and preparing to print the 50D image, I thought I'd shot it with the 5DII.... until I looked at the EXIF.
So IMO the crop camera comes pretty darned close to FF, unless you're making really big prints from the images. I find the newer 18MP models' images need considerable more sharpening to get the same kind of detail as the 50D or 5DII produce straight out of the camera... The newer 18MP APS-C croppers use a much stronger anti-alias filter, that makes images look soft initially. But the detail is there, it's just a matter of post-processing to bring it out.
You also can stitch together shots from either crop or FF to make much, much bigger final images. Check out
GigaPan
.... George Lepp has recently been doing gigascapes with a 5DII... as many as 200 or more separate shots combined into a single final image that ends up well over a gigbyte (8 bit). He has lots of info and some
example images in a recent article in Outdoor Photography magazine
. Heck, you'd need to shoot with 8x10 or larger film (or digital, if it existed) to come anywhere close to the sheer resolution of these. And you can potentially do the same on a slightly reduced scale with a 50D or just about any other camera of your choice. Just think how fast you'd fill up hard drives, with images that are over a gigabyte each!