I tried this tonight in my 2.6 auto. 4 runs on a quiet road....
1) Sport Mode on - 9.3s
2) Sport Mode on - 9.3s
3) Sport Mode off - 8.9s
4) Sport Mode off (and climate off, forgot about that b4 the last run) - 8.7s
Should i be disappointed by this, or is this about right? It did have a full tank of fuel, and 6ft 7 / 21stone worth of FB driving it...... 
Not bad but not good, mine was a hire car though originally!!!!
Done a run today 9.0 seconds, slight drop of power at full revs over petrol, but need to get the gas system recalibrated!
BP Ultimate does work hence 7.8.
If I want to go mad I'll use petrol, but gas is so cheap a slight power loss is no worry.
It would be a good test to see what decent fuel will achieve - mine was on Asda special mega cheap rubbish, 95ron. Might try a splash of Ultimate and see... ...or the 102ron they are selling in MK....
I was pleasantly suprised yesterday, bit annoyed today. BP Ultimate did work on mine, I was expecting maybe 1/2 second slower on gas. But I will make two points.
Full revs, gas not as good, but at 5000 nothing noticable, off the line a little more delay.
The DBW does not like stall speed launches as if you are slightly slow it cuts the throttle.
I think the 5000-6000 section cost me 3/4 second, slower launch 1/4second - very rough figures (I will try again tonight on way home if I don't go to DIY shop)