"JoeinTX, if the offset were to weigh 23% more than the tandem, then which disk would perform best? If they weighed the same, then which type performs best?...."
If the offset were 23% heavier, then it would work better than the lighter tandem if they weighed the same and had the same disc spacing. The converse if the tandem were the heavier.
"Here's a question for anybody that might have an answer. You have two 8' disks, both weigh 1000lbs each, both have 22" notched blades, both have the same angle on the blades. For all intents and purposes they are the same disk. One disk is offset and one is tandem, both are 3ph disks. Which disk works the best, digging deepest, leaving the ground the smoothest, etc?..."
Assuming the two are identical in all aspects other than the arrangement of the disc gangs..........I don't see any difference in them from what I've experienced. Same weight, disc spacing......the same amount of down force is being exerted per disc.....same ground pressure....just using a slightly different pattern for turning the ground and flipping it back.
With any disc it's going to be about ground pressure-two 8' plows (tandem or offset) but one with 6 discs per gang and the other with 8 discs per gang and the former is going to be a better true plow penetrating the soil and turning it over while the latter is going to be a better preparation tool busting clods and cutting plant growth better regardless of disc type.
On top of these two types, a company called Diamond Disc Plows produced a third variation on the disc plow.......taking the common "X" style arrangement of tandem discs and reversing it having the disc gangs is a "<>" arrangement. It was only a gimmick and did nothing to effect the performance of the same basic tool. They are no longer in business from what I can research.
Look at some of the various discs produced for severe duty by Fleco or Rome or others........the common theme is greater weight on fewer discs for maximum penetration be they in a tandem or offset configuration.
In short, what do you want? Do you need a ground turner or a ground preparer? For the first, the greatest weight on the discs and for the latter the more discs per given weight is best.
Same everything......number of discs....spacing...weight......no real differences.