VK1OD you have written a great article on the Budipole. 10% efficiency.
I am not sure that extraction of a single figure of 10% efficiency (which I assume you calculated from average system gain) is, in isolation, a fair picture.
The article discusses a specific Buddipole in a specific context, and principally its response to broadband non-directional signals.
I mentioned earlier that there were two main factors that influenced performance.
The modelled free space average gain on 40m is less than 1.5dB behind a half wave inverted V dipole, so resistive losses in the dipole and loading coils is not extreme.
The modelled free space average gain over ground on 40m is about 8.7dB behind a half wave inverted V dipole at greater height, so the effect of losses in the soil is much higher.
The message to take away is that the biggest performance disadvantage comes from the low mounting height (2.85m in this case).
In terms of a reality check, could I hear DX with it? Yes, I could copy DX in the afternoon opening to Europe quite well, albeit at lower S meter deflection. Lower system efficiency reduces both the desired signals and the noise and interference, so S/N is pretty much the same. Could I work them with 100W? No, lower system efficiency means my EIRP is down, and it would be even less if running lower power.
Back to the original question, I do not have a comparison of both a dipole and Buddipole at 40', but I do have a comparison of them in free space and at typical mounting heights. It doesn't strike me that the Buddipole was intended for permanent exposure to the weather, nor that it would survive high wind speeds... so those factors might make its deployment as a permanent station antenna at 40' impractical rather than poorer performance, not to mention the lack of convenience for adjusting the antenna for band changes.
It is a case of horses for courses, and my own opinion is that the Buddipole is not suited to mounting at 40' as a permanent multi band station antenna.
PS: for AA4PB, the purpose of the study was to discover how field strength measurements of noise and BPL emissions made on a public street with a Buddipole could be extrapolated to a typical ham backyard dipole. The studies performed fed into the standards bodies working on emission standards for BPL, and they seemed to understand and accept the approach. Whilst the traditional approach is to use EMC receivers and portable loops, they typically do not have a sufficiently low noise floor to measure ambient noise on all of our HF bands, so a better antenna is required.
Whilst the EMC reciever / portable loop allows a scan of all of HF in three axes in just minutes, the collected data often just documents the instrument's own noise floor rather than the ambient noise. The Buddipole was much slower, needing to be tuned to each measurement frequency, but we could and did measure ambient noise above the system noise floor.