Hmm, I don't know that the effiency matters much.
The wattage is based on DC side - so an 850 Titanium will deliver the same 850W that a 850 Bronze will -- they will be identical as far as the computer load you can throw on them goes.
Granted, the bronze would pull a bit more from the wall... but it's only a difference of 8% (82% vs 90%) - or 80W... at 85%.
And if you have no qualms about a 500W+ Graphics card or 250W+ CPU (Not saying you personally Grim, just the general "making a point") -- then that extra 8% is nothing. Maybe if you are rocking one of those 1500W+ PSUs, and then that extra 8% may be the difference between throwing a breaker or not - and that would be a legitimate reason for a gamer or home computer user to care.
Buy a power supply for the voltage quality, the warranty, the bells and whistles that you like -- but the Plus rating is mostly just a marketing badge. It might matter in a server situation where it's going to sit under load for long stretches of time (like 24x7), or maybe if you are mining full time, but it needs to be on at a healthy load for a long time if you ever want to recoup that price difference.
I'll grant you that higher tier PSUs tend to be better units, but it isn't because they are higher tier rated. The tier rating is a good reason for the manufacturer to put a higher markup on a product, but you shouldn't pay extra for just that. Pay extra for stuff that matters, like good voltage quality or cable management or 10 year warranty. It's a shame that stuff is hard to sleuth out if all you have is the box on the shelf to go by - which is why I love sites like this one.
