Used 4 to door, and tried a 2.5 to the door. 5 techs, and myself all noticed a difference immediately, and all decided it's easier to pull one 2.5 than 2 - 2" and went that way. The mytee cuffs ROCK! and set-up time is actually less than 4TTD. It's the last on first off the reel.
Nobody here has mentioned what size connect and hose/s is/are between their waste tank and their 2.5" hose - I think that could be the difference maker for those that tried it and didn't think it made a difference.
Apex D - has the 2 - 2" lines going from the tank to the machine's vac inlets. plug one up, connect a 2.5 to the other, made little if any detectable difference.
Bought the new "wing" for an apex gtx d - flipped it backwards, so the 2 - 2" vac inlets connected to the 2 - 2" vac lines going to the waste tank, then on the other side (manifold side) directly connected the 2.5 - big difference noticed immediately.
If you are using a TM that has 1 2" from tank to 2.5 connect, you are going to have to alter your tank and get a 2.5 inlet to get the full benefits imo. If you have two, you'll need to use both.
A bigger straw won't make a chit of a difference if there isn't more suck at the end of it.
Like a few have said - what works for one, may not work, or work well enough, for another to make the change worth it - look at your system as a whole, determine if it, your van, your protocols, and your TM are able to make it a viable option.
We have tons of spare room in our vans, so we have the 300' reels, we keep 200' of 2", 50' of 2.5, and a spare 2" coiled up in the van if 300 is needed. Our tm's all have 2 2" vac inlets on the WT, or a 3"er - so for us it makes sense and we've consistently seen faster dry times, especially on frieze and berbers.