The BAC 1-11 simulator was a 'step up' after my huge analog choppers
Lots of ex rotary pilots in BA and it doesn't take long to get back into the fixed wing groove. Remember, you are going the 'easy' way round.
As to the sim assessment, they are not 'generally' looking at you being able to fly a 747. If you could do that then Willie Walsh wouldn't be moaning about training costs all the time. Trawl the thread and yo will see that the sim is about 'being in the ball park' flying wise and good crew co-op and the ability to take constructive criticism and learn from it.
Have fun