First I fine tuned the ROI as small as possible; with the used setting the ROI for H-alpha is now 125pixels.
Next I changed SharpCap settings: memory usage for camera maximized and camera control setting all max eg. Turbo on.
WIth and without the USB hub I was able to get to 400pfs and keep it stable during capturing.
Setting
TLAPO80/480 with Sol'Ex pro and 678MM camera
Herschel Wedge
USB hub connected with Camera and external SSD
Software: SharpCap, Inti and CS4