First, the Pentax 55-200 isn't very good. There are better alternatives, like the Pentax 55-300 and the Tamron 55-200 Di II LD (which is also available for the Sony.)
Second, the Sony A450 doesn't actually have 'Live View' the way that the Pentax has it. 'Live View' in the A450 is only for checking the manual focus setting.
Remember that 'Live View' isn't very useful for dSLRs. DSLRs are bigger and heavier than P&S cameras, and so holding them out away from your body so you can compose on the screen can get old quick. 'Live View' is handy when the camera is mounted on a tripod, and that's when the 'Live View' in the A450 is intended to be used. And while the A450 can't AF in 'Live View', the Pentax uses contrast AF in 'Live View' which isn't very good anyway. (The Pentax and the Sony use Phase Detection AF when using the optical viewfinder, which is much faster and much more accurate.)
The Sony has a 14MP image sensor and can stoot at 7 fps, while the Pentax has a 12MP image sensor and can only shoot at 4.7 fps. The Pentax can record video and runs on AA Batteries, while the Sony uses proprietary Lithium Ion batteries and can't record video.
- The lens is the thing.
- 'Full Frame' is the new 'Medium Format'.
- "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.