Agree that it could be a blocked CAT - however the rotten egg sulphurous smell does not mean it is Knackered in it's own right - brand new cars often have this smell from the CAT and it is normal enough at certain temperatures.
a very basic and simple test for a blocked pipe is - yes you guessed it - hold your hand or piece of paper at the tailpipe, and have a friend blip the throttle - there should be a noticeable surge of gas with the rev - if it remains constant - it is likely blocked and is choking the engine.
The reason I didn't think it was a CAT problem was that the _carouser stated - the engine does rev out, but that it felt like it was not getting to the wheels.
Blocked CAT's usually do not allow the engine rev freely - usually they struggle to get over 3,500 / 4,000 revs.
That's my story and I'm sticking to it