first, check the plextor forum for more info on the capabilities of the plexwriter.
if the plexwriter can do SD >2.51 depends on model and even unit.
for example i had a plexwriter 40/12/40S at home that did SD2.8 without any help from any program and the back-up verified in every drive i tried it in. but on my work i had another 40/12/40S in almost the same system and this one couldnt even do SD2.5 with out the help of AWS or EFM bypass option.
so you need a whole lot of luck when buying a plexwriter, one unit can do virtually anything the other almost nothing.