I have to say that I don't know that I've noticed any difference in lag times going from an aquarium pump set up to bottled O2.
I suppose this is an opportunity for a side-by-side fermentation just to see...
I doubt you would in average-gravity beers, but I'll bet it makes a difference in REALLY big brews.
I just went with O2 because it was basically the same price AND I could buy it from the LHBS instead of Lowe's, etc.
I'm due to brew up some of my stout, which is typically around 1.080 so it might be a decent candidate for a comparison.
I went to the O2 system (over the aquarium pump) as my I typically brew bigger beers and I wanted to be sure I get a good fermentation, particularly in my old ale and my tripels. And my quad, and my big stouts... And my BDS. Etc...
I never had poor fermentation with the aquarium pump, but I suppose I had $$ I was looking to spend and went with the O2.
I use the aquarium pump now to start my siphons when I keg, which is very handy. I suppose I could use CO2, but the pump works fine for my needs.
If I do a side-by-side I'll take notes and post back.