Guys who pull 75' hose runs, will see the least difference, that said, I think i would still prefer to have 100' of 2.5 on the reel and what ever 2" lead lengths I felt comfy with (ie:25' or 50'). That way i can just pull and go.
One hose regardless of diameter is less hassle than 2, day in and day out, 4 jobs a day, 90% of teh 2.5 club started out with 4 to the door in one form or another, they "opted" to dump the 4, and go to a single 2.5 after having experience.
MeAt is right though, correcting defficient tank plumbing makes a big difference, even if you only run 2" hose, cause on a short run, everyones TM sucks good, you don't "need" 2.5, you just need a full unrestricted 2".
The 2.5 earns it's keep at 100+ feet.
I think Albert does a lot of short hose runs, if he's put the big hose to the back.