So based on a request from folks on this idea (GCMonitor metrics - Support IBM MXBeans for IBM JVMs), I went ahead and created an updated GC Monitor specifically for IBM JRE.
This particular one was tested against WAS v7.0 JRE 1.6.0_2.4.
It basically looks like the OOTB extension and that was done on purpose to leverage the typeviewer. The image shows some of the additional metrics which this extension provides.
I did not find many other metrics I thought would be interesting to display. If you find any based upon the APIs, let me know.