So essentially unless you are building something for power "4.0 stroker" there wouldn't be too much benefit due to the only other options being other bolt-ons like exhaust, intake as well as the intake spacer.
Tricky answer, the 3.5 cams have 238 degrees of duration and .337lift on the intake with 252 degrees of duration and .257lift on the exhaust side. The 4.0 cams have 244 degrees on the intake with 354 lift, the exhaust has 262 degrees of duration with .275 lift . So with that if you have 3.89 gears and other bolt-on items it would run better. How much better depends. If you have to replace the cams anyway I would use the 4.0 cams. Personally ,I'm getting ready to rebuild a 3.5 and I will be using 4.0 cams, .030 pistons, 3.89 gears and with a larger TB, nothing to radical.
Sounds like if you are in the area it would be a nice upgrade, but if you aren't in the area it might not be worth it. Keep us posted on how it runs! Might be something to look into without getting to radical with the 4.0 stroker concept.
I was under the impression that where the gear pressed onto the shaft it was different? Like a "D" shaped shaft as opposed to a keyway? The motor I'm building will be an '04 3.5 out of an SXT. It will be running 2.7 tranny gears, an '03-'04 Special PCM, a V3 intake spacer and max-bore bored throttle body.
I had the 4.0L cams in my 02 trep. Didn't notice much in gain. However on a trip to Daytona with Intrep_Ed the car didn't like to hit 80MPH. I thought it was some other gremlins with the car but a couple of peeps at the Daytona meet said it could be the cams.
I wished I had a chance to dyno the car but never got a chance from when the stupid timing belt snapped prematurely. So if yo do toss in 4.0 cams I would get it on a dyno.