Titanium is just one measure of a efficiency which is important, but there are a bunch of other important factors, regulation, protection, ability to handle ripple etc. Though not sure what the tier list is, but assume that is the reason.
The Corsair SF750 unit, does the latter bits very well. Its why I jumped from the 700w silverstone to the SF750w unit as the formers ability in other areas from reviews looks better and I was trying to get rid of coil whine with the 3090 which you want as low ripple as possible. went through dozen of reviews as no single one compares them side by side. The 700w Silverstone unit in itself had no issues powering my 9900k + 3090FE when looking at power from the wall draw but the coil whine did hence looking at the units in more detail. The 800w unit looks to be slightly beefed up vs the 700w but does lag the corsair in areas mentioned above.
In normal use so gaming, with my 3090 pulling 400w, the CPU will only pull about 60w-125w or so depending on game (rarely maxed on CPU), and rest of the system around 50w or so. In effect will not really go above 600w or usually 550w use all that often when gaming. Only time you may is if your 3090 model has a higher power target BIOS and your stress testing it + a lot of voltage on the CPU and stress testing that with say an AVX load at the same time. The 3090 can have heavy spikes now and then which catch's lesser PSU's out, but non-issue for either of these units. TLDR, would not really worry about either unit, they will be fine, but given factors I have seen aside from efficiency and how coil whine did reduce with the corsair unit swap, would be my pick.
- thanks all