Based on examining the hot cam profiles, the exhaust is generally hotter by 10-15°, and assumes the same rocker ratio for both.
Current thought is that lift is far more important on the intake valve than the exhaust (where the opening point is the single most important factor), which means that (although consistency is always good) more lift isn't cost effective, especially if it means making a very different piece (ref: geo angle).
However: if you only do the intakes, that automatically increases the intake's effective duration, especially the overlap - so it reduces the in/ex bias.
No easy answers.