Matt,
Yes and No,
What are your dry times? 1-4 hours there is not much going to be gained in that area.
Do you do apartments or second floor set ups where YOUR 42Dr lands in a awkward spot? ( second floor, staircase going up ) and if it does then you just set up 42dr at bottom and run 2" the rest of the way? If so then your not gaining anything really.
Are your cuffs AIR TIGHT ? More cuffs that are leaking in a 42dr setup is going to affect your actual lift at carpet....
AT / VT tm's don't count they have soooo much cfm it doesn't matter.
This is another thing that opened my eyes to 2.5 vs 42dr
My older son was helping me....I was always onto him to SLOW DOWN with longer runs of 42dr you need to understand " LIFT LAG " becomes a real issue. Meaning that if the blower doing the work is too small, this set up is like adding more cubic feet to your waste tank....a bigger tank takes longer to put under vac than a smaller one....we actually got called back because we had carpet that wicked back due to to much water being left behind, he would just not slow down enough to keep the system under proper lift....
So I put 50' of 2.5 back on the van solved the problem the "LIFT LAG" was cut down enough to remove more of what he was putting down, he was still to fast but it got it back into more of the normal removal range.
If you are going to go 2.5 don't cheap O on the hose, I only know of AMFLEX and because I have used it I can tell you it is more flexable than some stock 2.0 that comes with some TM's. When I was all into this stuff the Amflex 2.5 was so fleaxable I ran it right to my wand ( I wouldn't do this now but I did at the time) The wrong 2.5 will BREAK YOU in a weeks time it is NOT easy to deal with and in the cold weather the coils as your rolling it up can flip and put a huge dent in a car that well you would have to pay for.....Its coiled strike is faster/ and as lethal as a King Cobra on a hot summer day!!!
Even if it is JUST to get distance unrolling and rolling onto the reel is a royal PITA, there have been many times my face and nuts have taken one for the team with some of the 2.5 I have now, I needed 2.5 and I got a good deal on it ( VWTM ) thinking ah it is just for flat run distance NOT SO like I said the wrong 2.5 is brutal.
What you will gain is faster LIFT LAG, faster set up times, and less likely to cheat on your setup ( not running 42dr due to awkward placement ) I have 75' of 2.0 that comes off reel first then when that comes off my 2.5 starts to come off, I have 50' of it broke into 25' sectons and I use what I need. This is on my PC legend and yes 2.5 is better than 42dr for this rig.