There's exactly 1 Titanium model >400$, the AX1500i, all others are cheaper.
There are only a few Platinum models in existence, therefore Gold is actually the highest efficiency. Yeah that logic doesn't seem to work.
Jonnyguru doesn't do continous load vs efficiency tests. You have to interpolate and they are within 0.5%, below his margin of error.
Also you don't want to go there, the efficiency vs load curves are going to be a nightmare. For example the GS and G2 are very close but dancing around each other. At low loads the GS, arguably the inferior platform is more efficient because it's peaking at ~40%, whereas the G2 peaks at ~50%. And that might only be due to the fan profile.
Yeah, don't go there.
With the G2 650 at 60$ and the P2 650 at 70$ (which will definitely be more efficient) I don't see it being a steal.
With the VSM 550, 550W being more than enough for 95% of all builds, it being even more efficient than either the GS or G2, it's hard to ignore at 50$. 10$ more for better ripple supression and a fully instead of semi-modular PSU even with marginally lower efficiency is a tradeoff worth considering, 30$ not so much.
Unless you need more than 650W the 650 P2 is better and cheaper than the 850 P2.
My point is get over that "look at that PSU, a gazillion Watts for $". You're not doing yourself any favours by getting a PSU more powerful than you need. For any build <=650W the 650 P2 is hands down the better choice, even if they were both at 70$. To be even worth considering in that case the 850 P2 would have to be cheaper than the 650.
I'm sorry but people will read "it's a steal" and waste 30$.