I haven’t seen that comparison yet… maybe because there are too many and no one has the time to spend to compare them to the commercially available tools. But it will be interesting to find out how they compare. Anyway you might know this but as far as the commercial tools there are some comparisons that you can find here: http://www.qadownloads.com/White_Papers/
That's a good question. I don't think anybody has done this and my guess is because large companies use load test results to 'post' numbers, and compare against each other. In order to do this, once needs to use 'established' tools.
Technical comparison between commercial and non-commercial tools is only one aspect you are looking at.
There are other issues like;
1. Non-commercial tools may not provide good technical support.
2. Non-commercial tool vendors may be using the opportunity to beta test their tools before launch by not attaching any license fee.
3. Generally the capabilities of non-commercial tool will be limited. If your requirements are met by the tool yes you can go ahead.