If you read my lens story in the blog section, then you know that i have gone through a lot of lenses for the Minolta / Sony Alpha AF mount. In my opinion, the Sony ZA 24-70/2.8 SSM is the most useful lens in this mount. The Sony Zeiss 135/1.8 produces better pictures, but for most uses, the ZA 24-70 is unbeatable.
As far as being a full frame lens...so? All lenses produce distortions at their edges. Using a full frame lens on an aps-c sensor utilizes only the "sweet spot" of the lens, producing pictures that are very sharp from edge to edge and corner to corner. This is a GOOD thing!
I had to work my way up from mediocre third party lenses to cheap primes to good primes and finally to top quality zooms. in my opinion, top primes may produce slightly better quality photos, but in most cases, my zooms will match good primes unless you really pixel peek. My zooms also offer me any focal length I want from 24-200mm (or the equivelent of a full frame 36-300mm).
Again, just my opinion, but I do feel strongly about my two lenses...I have not upgraded (or felt the need to upgrade) in SEVERAL years!