boy oh boy... what to post... do i help... or do i flame??
first.. a question... why are you just taking the car around the block?? from experience... its because you dont have a licence at the moment and you are getting antzy..
to really feel the boost... its better in 2nd gear.. the gear ratios are better and your max speed will still only be around 120km/h.. which if your doing the above question.. wont really matter unless a kid steps out in front of you.. the sheer velocity of doing it in 1st is hard on the driveline.. and your top speed is only going to be 60-80, not really worth it if your going to be an idiot in a surburbian street.
and the answer is dont knock it back into neutral... at 8000rpm, its dumping in enough fuel and timing to support the load and pumping enough oil and water around to handle the conditions... then when you knock it back to neutral, that all dies off... the engine and turbos get incredibly hot due to the lean running conditions when its all shut off like that, all that heat has nowhere to transfer to as the water pump has returned back to idle speed and the head now has copius amounts of oil floating around and none in the sump. the turbos are still spinning at 70000rpm and the oil flow goes from lots... to not lots.. so the not lots of oil in going through the extremely hot and still spinning turbos is going to overheat and lose its lubrication and cooling properties, at worst possibly carbon up and clog or restrict the galleries in the turbos
another thing to take into consideration with the gear ratios of 1st gear is the engine braking... if you punch it in first then let the revs die down, its so abrupt that it throws you forward in the seat, it can nearly lock the back wheels just by stepping off the accelerator.. its not good for the clutch, gearbox, driveshaft, diffs... etc..
so your best bet... if you really must do it... is get it rolling in 1st, punch it in 2nd, clutch in and then change to 3rd or 4th to let it wind down by itself so that everything is in check.