Just ran the numbers in our RTOW computer for the same weight, field conditions Flap setting etc with the only change being Flex v TOGA.
Flex gave a V1 of 19 kts faster
Flex gave a Vr of 15 kts faster
Flex gave a V2 of 13 kts faster
So flying at TOGA thrust but retaining Flex speeds is conservative and thanks to the document mentioned above seems to be ok with AB.
However that being said unless I had a very good reason to get airborne ASAP I would take a moment and re do the numbers.
