I can not help but comment on "Bluestreeks" attempted accurate comparison between the two types of carburetors, Holley and Demon.
First off you need to compare both brands with similar models, IE HP750 and Demon's Speed Demon, not the #4777 650DP, #4779 750DP, or #3310 750VS with the 750 Speed Demon.
What clued me into thinking you compared a 650 Holley or 750 Vacuum Secondary to the Holley 750DP is because those two Holley's don't come with down-leg boosters, only straight-legs. If this was even close of a comparison it would have been a Holley 750DP or a HP 750DP which does incorporate a down-leg boosters. On occasion the 750DPs due come with 2-corner idle but this characteristic is always found on the 650DP and 750 Vacuum along with straight-leg boosters.
Something I bet you didn't catch either is that the Demon does have a superior down-leg booster over the HP version because of it's double cut design, veiwed from underneath the carburetor. This provides a better fuel sheer or fuel atomization as most understand it, then the Holley HP version. Another awesome feature of the Demon is their changeable booster design, which allows booster changes all day long as per calibration, not performed at a novice level with Holleys.
With respect to Demon's external air-bleeds being larger, they are not. A 0.026" orifice, for example, is uniform among both brands if calibrated as such, it's just Demon's is recessed and Holley's isn't. The non HP versions of Holley do include press in air bleeds and are difficult to adjust without steady drilling, but can be easily converted with a 10/32 threaded tap. I'll give that one to Demon for out-fitting all of their carbs with this feature.
But the irony of it all is a too much information could be deadly because now you have adjustability that only a dyno enviroment should see from experienced hands. Sure you can tweak those air-bleeds at the track, and Demon frequently incourages their customers to do so, but how could one read the A/F spikes or dips within a certain RPM band, that's very important to know. But Demon must feel comfortable in taking that sort of liability, I know I am not.
Now the Demon does have externally adjustable secondary opening and Holley doesn't out of the box, but you can retrofit it with the modification for under $10.00 which allows track-side adjustment. But the good thing about it is once it's adjusted, Holley or Demon you shouldn't have to mess with it again.
As far as gaskets go, well that all depends on the material used. Demon's come with one type of gasket material which always tears when over-torqued, the same as Holley does on their blue gaskets. Now the HP version doesn't come with paper, only the 4779 and 4777 (just two examples). There is only one gasket I have used, and I still use to this day, and that's the green viton coated version from our supplier, hands down the best gasket in town. I would bet money that BIGS uses this component as well as we do. Those Holley Blue and BG Red (hmmm a little color theme going there?
)normally always...I mean always rip when over-torqued. The Viton greens do not, and we run alcohol throught them. Funny thing is they work for both Holley and Demon as well.
Now what I was trying to point out on my comparisons is that you need to compare like items, such as a Z-71 Chevy to a 4X4 Ford, not a Dodge Viper to a Ford Focus. That's just not accurate, it's misleading.
Now this is my opinion.....I think Demon out of the box are great carburetors in comparison to the HP Holleys. They require alot more tuning because of the blanket calibrated fuel curve they're delivered with out of the box, but when in the right hands they can really perform once manipulated. I have seen more box HP Holley's run clean out of the box "on the track" then Demons.
With respect to custom built carburetors, I could make either one better than the other, or even both run the same. Now it's also my experience that the Demon flows a cleaner more consistent fuel curve then the Holley only because of the billet metering design.
All in all....they aren't much different, and their isn't much contrast in price between the Speed Demon 750 and Holley HP.
I hope this sheds some light to the topic. I could care less which brand someone likes, I sell them both and I can tweak both to perfection.