There is a very good tutorial pinned in the XP section on slow computers, and most of it applies to those running Win 7.
In general terms, slowness can be caused by malware, a hard drive that is getting full (less than 10 - 15% of free space) and an excess of temporary files.
The security software you list should not cause any conflict problems. I personally don't like Norton, but that is a purely personal opinion. The important thing is that it is up to date with its definitions. Is this a 'free' trial version that came with the computer or are you paying them good money for it ? If you are paying them then you should be getting the updates. If you are still running a 'free' trial version I would recomend uninstalling it and replacing it with one of the free anti-virus programs like Avast. The same goes for Super A/S and Malwarebytes, except these are both free. I presume you are running scans with these from time to time, and updating the definition files each time you run them ?
Another program I like - also free ! - is Piriform's 'CCleaner' for getting rid of temporary files (www.piriform.com). Just two points with its use. On the second page, 'Applications', make sure the box against 'RegEdit' is unticked, and secondly, DON'T try to clean your registry.