I'm gonna zip past everything else in here as it's either subjective, misinformed, or a diagnosed bug.

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Applications that have been installed but are not running cannot have an impact on how responsive the device is. Only active applications can have an impact, and it will be on one of the following:
- CPU Utilization
- RAM usage
- Disk IO

If you think a recently installed application is causing the slowdown, you should see a speedup after uninstalling it. It would be easier to identify the "issue" if you could describe when it occurs and what you are doing.

No, the damage due to forcing electrons through the copper interconnects inside the CPU at a higher clock rate will be far greater, as you (hopefully) aren't trying to run games and other cpu-intensive software for long periods. You shouldn't be overclocking anyway, that's the only thing I've ever seen people from Nokia ever say "don't do it, -that- will void your warranty."