W3 Total Cache does speed up performance. keep in mind that performance may reduce if:
- You use other optimization plugins
- You use too many plugins external from W3 Total cache. (This said because it also tries to compress the plugin's features as well so the resources that's needed for one plugin would be increased about 0.3 - 2% higher).
Just keep in mind of how many plugins you are using at the same time.
This shouldn't be a problem for the time being. It just depends on what theme you are using and how many plugins you are using on that theme.