I believe this came up before and the bigger concern wasn't all out dry performance, but the loss of wet traction for on/off track purposes.
Thanks for the comments on flipping- I agree, there is potential loss of wet traction for the front tires. Think about this- When I did have the normal front tire orientation I noticed that the front inner tread blocks were wearing out in a hurry. In no time the separate blocks loss their pattern and resembled a worn large block/slick surface with minimal partial side ribs- in that condition how well do you think that tread pattern works to dissipate water effectively?
I have driven with stock runflats for autocross using the normal tire orientation (new and worn) and with the flipped front tires (newish and worn) and I don't notice any real difference under dry conditions. Even with mild wet conditions there seems to be little difference. My run times are within about 1.5 seconds of using R compound tires on a 30-35 second course. This is using swift springs and stock swaybars and with whiteline adjustable front and rear swaybars.
I have driven on the street under wet conditions using the flipped front tires and have not noticed any loss of traction when driving at reasonable speeds.
Due to the lowered suspension and adjustable swaybars there is minimal understeer that can be controlled during performance driving and literally no understeer in street driving under normal conditions (using flipped front tires).
The Asymmetrical tread pattern on all GTR runflats is designed for allowing increased stability in cornering (due to larger outer tread blocks) and better dissipation of water (smaller inner blocks).
If you are tracking your GTR then you'd be better off using the normal tire orientation. If you only street drive then you can choose to flip the front tires to get up to twice the tread wear and save a little on replacing the front tires so soon. If you live in a dry climate then you have less to worry about with loss of wet traction- however you can easily drive in the wet but you do have to use caution and be reasonable.