I don't want to get into a debate about how long it takes to blast a body as there is no correct answer (things like layers of paint and bondo can greatly effect time). A courser media, higher PSI and larger blast tip are all ways to increase your stripping rate and reduce blast time. All of these will also increase the risk of metal damage. We focus less on speed and more on the process that produces the best profile on the metal for priming. Our goal is to leave a "very fine" profile (similar to the feel of a piece of very fine sandpaper) on the metal. This is great for primer adhesion and does not require any additional metal work or high-build type primers.
Each blaster will have their own process and results will vary. We have sample blasted pieces (hoods and deck lids that are long and flat) in our showroom that our customers can examine and feel, before they choose to have us blast. This allows them to see exactly what they will get back. My recommendation is that you ask your blaster to provide you with "samples" before they blast your body so that you can be comfortable with their process.
As for acid dipping vs. media blasting, we just had a '68 Barracuda in 2 weeks ago that was acid dipped. The biggest concern with this process is actually neutralizing the acid after it is dipped (so it doesn't eat your paint). I am not an expert in acid-dipping, but I can tell you what we learned:
1. It is expensive and there are not too many people that still do this (at least in New England) due to EPA issues. My customer paid $2500 to have the Barracuda dipped.
2. He ended up bring us the car with the rocker caps removed so we could blast inside the rockers....there was still acid in them!
3. The acid will eat the metal. There were several areas on the car that were pitted by the acid.
4. How do you get material back into those places not exposed?
Now the down-sides of media blasting:
1. Not done properly, metal can be warped/damaged.
2. Dust and media everywhere! The car needs to be blown out REALLY well after. You will find media even after you think you have it clean. And it is a pain...I am not here to hide this fact!
Here's a before and after on the acid-dipped Barracuda:
...The car had sat for 30 days after the acid-dipping and had flash-rusted.
I hope this is helpful. I am not here to debate media blasting techniques, just share our experiences and help guide and educate!