(Post #3)
 
I just got my new Scarlett Solo and Sonar now informs a latency of 563 samples (12.8 msec for 44000 Hz, 11.7 for 48000, 6.4 to 88200 and so on).
I wonder if this latency is correct or whether can I reduce this number?

Hi. Are you using the Focusrite ASIO drivers? I believe that while recording, or when projects are reasonable size, you could get lower. Try going down to 256, or even 128 during the recording phase.
You do not need it to be that low for mixing. For that stage, you can / could up the buffers to as stable as needed (1024 and up, if necessary).
Best of luck.

I'm sorry, I forgot to adjust "Asio default buffer size inside" inside Focus Scarlett Asio Control Panel, for mode "Recording". 
Now I have up to 155 samples with 48000 Hz (3.2 msec).
Very good.

Nice That makes a difference, I would believe.