I am around the 330 mark and the diference when i put the headers on was very big.
I was well happy with the performance before the existing headers fooked up,car has always been really responsive and great fun to drive.
I know ported standard headers have there benifits,but mine responded so well to stainless jobbies.

Plain and simply,if i'm not going to see or notice any diference between heat wrapped or not heat wrapped then i not going to bother.
p.s
my standard headers were well fooked by the time i got them off.