Here's my take. I've owned an 02 ETH with an EZ and I currently own an 04 ETH bone stock.
the torque output band is narrower for the VP44 engines, hence the limitation for peak HP. EZ fueling on my 02 made it feel more responsive than my stock 04 for two reasons:
1. in the 02, the EZ makes torque come in very quickly at low rpms -- well over 150 ft lbs gain at 1600. so you have a boat load of power off the line
2. The throttle position data is interpreted differently in the 02 and has a natrually very responsive throttle. This has been calmed down considerably in the 04
So an 02/EZ will jump off the line compared to a stock 04. But peak horspower of the 04 is about 60 HP greater than the stock 02, and the EZ/02 will only approach, but probably not exceed, the peak 04 HP. Thats just because peak HP is at high rpm (2900 for the 04).
The 4. 10s give you about 10% more zip at low speeds due to torque multiplication. Definately not dragging you down unless you are trying to achieve a top speed at a high rpm. I would expect the EZ box on the 03 would outperform an EZ/02 combination by a margin that would be easy to detect with your seat-o-pants meter. But, alas, I have not driven a 3rd gen with an EZ.