As I mentioned in my previous posts, i'm going to be putting a spray booth in and there are alot of decisions to be made. I've sprayed open air primarily, but I have rented a booth here and there, however, I never really painted in a quality downdraft or modified downdraft booth. There honestly isn't a substantial savings either way, it's more about the amount of room it consumes.

So, is there anyone out there who has used both configurations that can give me some insight on functionality of the two? Will I honestly notice a difference?

As to a modified down draft, are you talking about exhaust on the ends?
If this is the case I haven't used this type, I have used a cross draft in the past but for the past 15 years my booth has been a down draft type.

I can see their would be a cost saveings with a modified type, you would not have to dig a pit in the floor for the exhaust.

I've worked in many different types of booth, old & new, good & bad.

In order of which is best (in my humble opinion) a full downdraught has to come top. Then there was what I think is called a side floor. Top inlet with full length extracts along the bottom of the side walls. Very similar to a full downdraught if you can't have a pit. Then I'd say rear extract, with a side extract being bottom of my list.

By "best" I mean in terms of uniformity of airflow and temperature throughout the booth. The side exit one I was in for a few years was terrible for this. The warm air would flow in from the roof and straight out to one side, leaving lots of dead cold air on the opposite side. So when clearing one side of the car could be hand slick ready for another coat and the other would still be wet enough to flow. A recipe for runs!!! Working in there did teach me a lot about reading a booth though and figuring out where the dead spots were, but clearly not ideal conditions.

There are always going to be compromises though, either through space or budget, so you may find a less than "perfect" solution might actually suit your situation best

The modified downdraft i'm speaking of is like this..
www.accudraftpaintbooths.com/product-details.php?r_ID=8
The exhaust in two columns on the back wall.

also, I will get a downdraft booth with the optional basement, so I don't have to dig a full pit

I've used down draft, cross flow and semi down draft (similar to the one in your link)

I agree with Andy, a true down draft is by far the best...

The cross draft can work very well, you just need to get use to working in a certain direction.

The semi-downdraft I used, I did not like. The intake was in the ceiling near the doors, and the exhaust was the entire back wall. Air flow near the door was very poor, especially if you had a car in there. The part of the both that was central towards the front of the booth (where about the hood of a car would be with a car in the booth) was the dirtiest part of the booth. Just spraying parts, the booth was ok, but once you had a car in there it just screwed the air flow up and made a lot of uneven areas.

One thing to keep in mind, no matter the setup of the booth every booth has its quirks as to where the uneven spots are, even down drafts. It just tends to be much less of a significant difference in down drafts, especially as you load the booth up.

True downdrafts are the way to to go if it fits your circumstances... Semi-downdraft booths with full ceiling intake, and the exhaust on the floor along the side-walls of the booths also work VERY well (just a bit more turbulence from a full downdraft). The semi-downdraft (modified downdraft) booths with the exhaust in the front (or front and rear) are no better than a cross-draft IMHO... Keep in mind though, if you are looking at a true downdraft, and are going to have a pit dug, I highly advise thst you have at least a three column filter pit. It will cost more for the wider pit/grated floor, and you will have a little higher maintenance/filter cost, but when you have a full ceiling intake, you don't want to choke down the exhaust (creating significant turbulence/dirtier jobs) by only having a single or double row pit. Having a full exhaust floor is the ideal way to get all the benefits of a true downdraft booth, but if that is too much cost/maintenance for you, at least do a three row/register floor pit (just a bit wider than your standard passenger car). Good luck!

I know what you are going through, I am in the process of installing a new Garmat chinook semi downdraft paint booth this week. They advertise it as a self contained downdraft. Due to my building limitations it was the best option for me as far as fit goes. I will let you know how it performs after I actually get to use it next week (hopefully).

when you say semi downdraft.. is it side downdraft? or rear exhaust?

It is a rear exhaust. They finished the cabin yesterday and over the weekend hopefully the electrican will have it wired so we can fire it up next week. I will try to add pics. next week.