Here's the definition of "profile overhead" from within P3:
The load time spent profiling code. Because the profiler slows down your load time, it is important to know how much impact the profiler has. However, it doesn't impact your site's real-life load time.
Please let me know if you still have questions or if there's something that needs further clarification.
As for how to speed up your site, I see:
MySQL Queries: 229 queries avg.
This is really high. You should look at the "Detailed timeline" to see which pages cause the most queries and investigate appropriately. In general, plugins like "related posts" are going to cause this number to go up.
Number of PHP ticks: 79,049 calls avg.
This is basically a measure of how complex your site's code is. A stock 3.8 WordPress site with the twentyfourteen theme and no other plugins is going to be 1,000 or fewer ticks. Obviously more plugins means more complexity means, but it also means more CPU usage and more time to load. You should look at the pie chart and the detailed timeline to figure out which plugins are causing the highest impact on your load time.
Memory Usage: 72.63 MB avg.
This means you're using a lot of memory. Generally this means you're loading a lot of files. This can happen with complex themes (e.g. theme frameworks) or complex plugins (e.g. W3 Total Cache) or just having many plugins. By itself, memory consumption isn't bad. It becomes bad when you hit memory limits. This number is just an indicator that your site is complex and reducing the complexity will increase your load time.
A note on P3 and W3 Total Cache:
The way P3 works, it bypasses W3 Total Cache because you're logged in. If you want to make your site faster for anonymous visitors, W3 Total Cache is great. You'll need to make sure you're using it correctly though. If you have the money and inclination, W3 Edge does offer optimization services. This is not an endorsement, I have never used their services, I just know they exist. To get a true measure of your site's performance to an anonymous user, use webpagetest.org.
If you want to make your site faster in the admin section, you can look at upgrading your hosting, or disabling more plugins, or working with your host on further optimizations.
I hope this helps.