Without having data of ex manifold vs inlet man pressure at low load levels, there is really no way to know how much difference to the off boost torque developed. However slight, a reduction in ex man backpressure would allow an increase in cam overlap, and volumetric efficiency. However saying that, rb30det's tend to get significantly more power with no boost (usually 130rwkw) than a standard rb30, even with their lowered comp ratio. This indicates the backpressure of the turbo doesnt significantly affect developed power/torque. I think it would be interesting to see how much could be gotten out of a gcg/slide highflow with the WI, as from my experience they seem to end up running into detonation problems when trying to give them any real timing, especially on the NEO