Q1. Information explaining IE8 javascript engine and how it is slow compare to other available web browsers / limitation as in functional wise (eg due to certain features of javascript engine, only xxx can be achieved)

A1. I googled "IE8 javascript performance"
I had many hits such as: http://www.tomshardware.com/reviews/windows-xp-web-browser-performance,3167-7.html
and
http://www.tomshardware.com/reviews/windows-xp-web-browser-performance,3167-7.html
which shows a benchmark where Firefox 11 was next slowest with a score of 559 and IE8 has a score of 57.   This shows that IE8 is almost 100 times slower than the other browsers.

An older benchmark shows a comparison of Firefox 3.6, showing IE8 four times slower
http://force5blog.com/technology/how-fast-is-ie9/

Similarly, IE8 is slow on DOM updates. A benchmark appears here:
http://stackoverflow.com/questions/6817093/but-whys-the-browser-dom-still-so-slow-after-10-years-of-effort

Operations per second:
Firefox 4: 510
IE8: 73

Q2. Information on why RTC Web UI run slow only with IE8.

A2. The Web UI loads the dojo toolkit plus thousands of JavaScript classes which must be parsed and executed to run the RTC web UI. The entire RTC Web UI is run in JavaScript (except some Flash reports). Excluding network latency and relatively short server response times, the performance of the RTC Web UI is directly proportional to the browser JavaScript engine speed.

The Web UI has been optimized to improve performance in the code, and the
JavaScript is compressed and pre-processed to be optimized,  but IE8 will always be slower than more modern browsers.

Q3. Any pointers?

A3. Refer to "Observed Memory Leaks When Using Internet Explorer 8" section of the RTC 3.0.1 release notes