I like to refer to this issue as "red-lining". For the next generation of products we are working on building more of these types of features into the product. I don't have the information when these features will be available but suffice it to say it will be fairly soon as this is not a uncommon reuqest. On the 4.x platforms there were platform architectural limitations stopping us from accurately determining red-line situations.
As for CPU metrics, this is something we are also adding in future versions but is not available on 4.2.
I try to answer as many product related questions as possible here but when it goes too far beyond the development of iControl applications you will get better support and more reliable answers by contacting F5 technical support directly. Their specialty is with questions like this.
F5 Technical Support
Email: support@f5.com
Phone: 206-272-6888
Web: http://www.f5.com/support/
AskF5: http://tech.f5.com/
Nimbostratus