I've just been through this process myself on a K20D.
1. Never completely happy with accuracy of AF, nor my MF abilities at f1.4-f2.0.
2. Took an informed punt and installed a Katzeye - much better in MF but front focussed enough to be annoying.
3. Installed 0.15mm shim (had 0.25mm), MF now spot on, results with AF also much better.
AF improvement has been the result of using the split screen to verify AF point selection. The AF system cannot benefit directly from the split screen, but the ability to see accurately what the AF is trying to focus on has led to a vast improvement in the ratio of in
ut focus shots.
No regrets, wish I'd installed one years ago.