You should not have any problems.
I used MC 4 for many years and ran some serious VST's and FX plugs in it. All of the plugs and FX ran perfectly.
MC has full VST compatibility. There might be the occasional third party VST/FX plug that doesn't run but most of the major company's products will run smoothly. MC6 is based on Sonar so there's a solid base underneath where it counts.
If you are running it in demo mode now, and it works well, the full version will run without issue. Some full versions actually work better than the demo's since they have to shut certain things off in some demo's..... depends on the company making the software and how they work their demo mode.