The EZ is a nice towing box with stock injectors. Personally, I'd look at the Diesel Dynamics TrueTorque Power Module (an EZ with DD-specific programming) if you're going with larger injectors. The TTPM's injection timing isn't as aggressive (i. e. , not as much advance) as the EZ, which quietens the engine and reduces peak firing pressures with larger injectors.
I haven't dynoed my truck since installing the DD2's, but AggieJustin has the same setup I do, and he's getting 342BHP/785 lb-ft on the dyno.
We tow a 13,500 lb 5th wheel that puts us on the road at 21,180 lbs GCW (21,500 lb GCWR). We never slipped the stock clutch empty or towing with the EZ -
until I added the DD2's. It would slip running empty if you floored the throttle at 1800 RPM in 5th after the DD2's went in. Others have run the DD2's with a box, and their stock clutches seem to survive. My point is,
if you're looking at an EZ by itself, the stock ETH/DEE clutch is normally fine, but with the EZ
and injectors, you may be calling Peter at South Bend Clutch!

Forewarned is forearmed!
Edit: Oops! I notice you have an ETC with NV4500, so some of my comments won't apply. I'll leave them for any ETH/DEE folks who might read this thread, though.
Rusty