Those equations on y web page are from Weber sizing formulas and other correlating information published from the 60's & 70's. As such they are guidelines and the factors provide a range of sizing possibilities to select from. I chose median factors but provide the range so you can make your own sizing guestimates. I have logged quite a bit of customer data for carb sizing vs. engine particulars. In fact, the carbs shown on my home page were custom built for an Italian customer who dyno'd his engine. It was 2.5 liter with GE 60 cams, twin plug and 911R muffler. It made 251 HP @ 7034 RPM. The Webers were 44mm with 36mm chokes.
My personal car had a 2.25 liter with S-cams, twin plug & 911R muffler. It had 43mm Webers with 35mm chokes and was a street car without driving faults.
Both engines had their Webers sized using the median formulas and both were happy combinations.
My formulas (from other sources) and my graph for venturi sizing seem to correlate to my customer data for engines from 2.0 through 3.4 liters with all kinds of carburetors sitting on top and for applications from street only through track dedicated cars.
I think Bruce Anderson's sizings are practical ones based upon easy to live with cars for street usage. I enjoyed my car as having a bit more spirit and that is how I set it up. Did 35mm venturis make a sizeable difference from 32mm or 34mm? I don't know or really care. I sized them in the same way the carbs were sized for the 2.0 S engine so nothing fancy there. The 2.0S was faulted for a peaky engine, larger displacement will tame the peaky-ness of DC40 (S-cams), the DC60s will want to rev higher to get the power and higher RPM means more potential to flow air.
So, 34mm for DC40 cams & 36mm for DC60 cams is what I would recommend as a starting point. Again, my 2.25 ran flawlessly on the street and had a very nice power band without glitches or making demands from the driver. I did tend to keep the revs at 3000 RPM during tooling around but that was not a requirement, I just liked driving it that way. I could put it in 3rd at 2000 RPM & feed the throttle without it bucking; this is with 35mm venturis in 43mm bores.
Something that can be done to maintain WOT power with a smaller throttle bore is to thin the throttle shafts which provides less blockage to air flow so 40mm bores with round throttle shafts will be more like 41mm bores at WOT.
Please remember that carbs are not EFI and typically do not like smacking the throttles open, regardless of configuration. Per Passini I paraphrase: Jet your carbs as you think they should be then "Suck it & see". If the engine is happy then fine, if not then alter jetting. The Dyno is your friend to assure WOT will not melt your pistons.
Most people don't get much benefit from having peak HP at 6200 RPM in routine driving and would rather a Solex cam for all around driving with more usable power through out the power band.