The mouse wheel on OSX is not behaving smoothly. It did in Studio One 3 and the first versions of 4, but somewhere along the lines of the r4 releases it got broke. I reported this before but guess I did not explain it well enough. Today I installed 5.1 and my first impression was that it was finally fixed which made me happy, in combination with the GPU upgrade.
But unfortunately it's not. I'll try to explain in detail:
When opening, move the mouse on the ruler. Use the mouse wheel to zoom in/out. I have a mouse wheel which iOS stepped, and every step of the wheel up or down responds with a zoom in or out, as expected. Very smooth.
Then I use SHIFT-scroll wheel to move the window view. It works as expected. Smooth on every single wheel change. But then, releasing SHIFT and trying to zoom again, very often it does nothing. I have to move upon and down on the wheel a few times before it starts responding. Of course resulting in overshoot of the intended zoom. When it then started to respond again, it stays smooth till I use SHIFT again or move to the arranger window to scroll my tracks up or down. Same glitch. It's like it's getting movement interia after using the modifier and I need to do a much bigger delta on the mouse wheel before it starts to respond again.
This all was smooth as butter in v2, v3 and the first versions of 4. And it's actually quite annoying now.