Hi Stefan,
what exactly is or feels much 'slower'? Can you please post more details or specific examples?
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In the meantime:
I'm assuming you're using the Focusrite 2i2 mentioned in your signature, right?
I'd suggest to check if you have the latest Windows 10 drivers for the 2i2 installed from the Focusrite webpage. Otherwise try to reinstall the 2i2 drivers, in general.
And also check for the latest graphics card drivers on the manufacturer webpage and install those manually (instead of letting Windows install these drivers automatically) ...
Going through some Windows Audio Optimization Tips (again) might also be helpful, in general:
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https://support.focusrite.com/hc/en-...-on-Windows-10
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https://support.focusrite.com/hc/en-...mputer-starts-
In addition, you can also try if making a fresh
portable Reaper install to a separate location (side-by-side to your current Reaper install) shows the same 'slow' behavior:
http://lacinato.com/cm/blog/25-reaperportable