Let’s compare two scales, C major and D major.
Which can you play faster?
Your first guess might be C major. It’s likely the first scale you learned, the most familiar. Even if you can play in all keys pretty comfortably, it’s not a bad thing to see a piece with no sharps nor flats and that is related to the C major scale.
When you test out which one you can actually play faster, it’s probably D major. Why is that?
The C major scale is theoretically the most simple. There aren’t flats. There aren’t sharps.
But regardless of how easy it is to understand and think about, there are actual transitions of notes in the scale on the saxophone that may or may not be challenging.
B to C is not the easiest transition to make clean.
Nor is C to D.
And C to D is the first transition in the scale! You move a lot of fingers and they all need to sync up perfectly.
Problems with the first transition in a phrase can mess up the rhythm of the rest of the phrase. And the first transition is C to D.
After the first transition, things are a bit easier, D to E involves lifting a single finger, as does E to F. Everything up to B to C is fairly straightforward. But B to C is a potential trap for schmutz.
D Major has two sharps, which isn’t the scariest looking key signature in existence, but not zero or one.
But let’s look at the transitions.
First transition is D to E. Involves lifting one finger. Difficult to do this incorrectly. Having a clean straightforward first transition is going to lend itself to the rest of the phrase being clean.
E to F
F to G
G to A
A to B
B to C#
C# to D
All of those transitions, except the final one (C# to D) involve moving a single finger. Very straightforward and hard to mess up. Very likely that you can do these transitions quickly and cleanly.
And C# to D actually isn’t as involved a transition as C to D. Your fingers often want to move together and C# involves no pressed keys while D involves most of your fingers being pressed. You move your fingers down together for the D without some of them being pressed already.
Therefore, you can burn through the D major scale much easier than you can through the C major scale. Physically it is easier to do.
It’s going to take a lot more work to bring the tempo up for the C major compared to the work needed to play the D major fast.
Think about the C# major scale and F# major scale.
Identify the difficult transitions in those two scales. Play through them, see where there are some problems.