The 737 in FS2000 does very nice loops and barrell rolls ;~) In 'real' sims, it will depend on the sim's accuracy of modelling outside 'normal operatons' envelope. Probaly not very accurate - why should they waste money modelling such flight phases?
In reality, any aeroplane can be barrel rolled IF DONE ACCURATELY - otherwise excessive speed and 'G' as the nose goes low in the second half. Loops depend on allowable 'G' (again, not too bad if flown accurately) but entry and exit speeds may be beyond VNE in large aeroplanes, especially in the 3rd quarter of the loop.
However, RAF Victors and Vulcans used to do a half loop with roll off the top in the 50s during 'lob' bomb practice. I've got it on vidoe at home from a Farnborough show of the time. Very impressive.
In the airline world, as well as the well documented 707 and Concorde barrel rolls, there was the 727 that performed extreme unauthorised aerobatics when the crew accidentally extended LE slats while experimenting with 1st stage of flap in the cruise. One slat was ripped off and the aeroplane 'departed controlled flight'. It was recovered by an aerobatically-experienced captain using 'parts of the attitude indicator not seen in normal flight'.
SSD