There is roughly only a 30HP/ft-lbf increase between the 4.4 and the 4.8is, so it wouldn't surprise me that test driving you would feel similar results.

N62B44 333HP@6100 332ft-lbf@3600
N62B48 367HP@6300 361ft-lbf@3400

I've only driven the 3.0 and the 4.8is so I can't compare too much. But I added the Dinan Stage 3 software and the 4.8is is off the line a lot quicker than it was with the stock software, and it transforms the car into something completely different.

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Jeff
Current:
'07 Jeep Wrangler
'06 BMW X5 3.0i

Former:
'12 WRX; '08 WRX; '06 BMW X5 4.8is Dinan S1; '02 BMW 530i Dinan S2