QSC makes a cached copy of any cab compressed drivers when you slipstream. (Quick Stream Cache).
for a few versions there was issues related to slipstreaming XP then 2k3 then BartPE. Some of the files were not cached and caused issues. That problem was fixed. So the answer is "It depends which version of BASE you use".
With M2 only the mass storage TextMode drivers are cached.
QSC is only useful if you intend to reslipstream the same packs multiple times. Otherwise it is of little or no benefit. It simply does not take that long to cab compress what few mass storage drivers there are. The reall benefit of QSC dates back to useing M1 when all the packs were CAB compressed and it would take an hour or so to do them. So a second pass would nto take an hour since they would nat have to be compressed again... simply copied.
If you are only making one disc there is no difference if QSC is off or on. QSC only benifits if you are doing multiple slipstreams with the same mass pack. even tehn it only saves you a minute or two based on your machines speed.
I hope that clears it up for you!
Jeff
publicly available test packs for mass storage are posted in the Mass Storage forum. They are only offered to users in direct response to posted issues. If you neeed a test pack post an issue you are having 
! (If you are not having any issues then you don't need one LOL)
.