I have X3 Producer installed and have Sonar Professional due tomorrow.
As it's a full license of Professional I can install it as well as X3 Producer so will that lead to problems?
I suppose I could uninstall X3 Producer and just keep the extras installed but if there's no urgent reason to uninstall it I'd rather keep it for now.
Thanks.

Hi. The short answer is yes  Go ahead 
All the best.

yup.

A bit of a longer answer: you can quite happily run multiple SONAR installations side by side without issue.
 
One word of warning - do not be tempted to uninstall anything once it is installed - you could easily run into all sorts of problems with shared folders/plugins etc and the amount of disc space you could reclaim is pretty negligible.

Well not completely without issue. I have all versions of Sonar I own on Windows 10. SPlat does seem to affect the older versions in odd little ways but they do function.