My stats comparing fame farm effectiveness between tiers. all runs have been 20 minute runs in the same undead dungeon following the same route, items (not tiers though) and spells.
gear as follows : broadsword, shield, soldier helm, soldier armor, soldier boots, soup. no aoe spells. premium active. gear tier is lower in red\black because obviously you don't want to go farm there in your 5.3 so that resembles "real life situation".
t5 yellow (5.3 gear):
t6 red (5.1 gear):
t7 black (5.15 gear):
i also died in t7 black on my way out of the dungeon because was a bit in a hurry and agroed 2-3 mobs (bigger than ghouls) which leads to a certain death at that tier. that 5.15 bought in the closest black city cost me 100k, so thats more than 2hours of nonstop farming to just get the money back
my conclusion after these tests is as follows:
the easiest way to farm fame solo is doing t5 yellow dungeons, because:
-you can bring your best gear of any tier be it 5.3 or 8.4 without any risk of losing it
-since you're in a higher tier gear the farm feels smoother without you running out of mana\hp ever and without having to drink a random healing potion
-you don't have to worry about getting ganked or aggroing too much mobs or making almost any mistakes because at this tier you are guaranteed to press your cooldowns and kill anything you have aggroed
-if you outgear the dungeon you are free to spec into any kind of aoe and just aoe farm since the incoming damage is low and you wont have risks or downtime. you CAN NOT do that in a t7 and probably t6. aoe farming t5 would probably be faster than farming t6 with 1-2 mobs per pull
money-wise the t6 and t7 gains are appropriately higher but I see them as "worth it" only in the current situation when the game is almost empty and you can run back to the black city without dying. if you get ganked in the dungeon or on your way back and your death costs you 2h nonstop farm, then t6 and t7 are not worth it, considering how nervous and concentrated the t7 farm is compared to t5.
what i would suggest or imagine as improvements (not necessariyl together implemented at the same time, just a list):
-link mastery tiers to mob tiers (aka t5 mastery only grows with t5 mobs, t6 mastery with t6 mobs etc). that would limit the "green\yellow safe zones" maximum achievable tier 5 and force people to "go out" if they want to level into wearing t6-t8 and mastering the items. we need more incentives to make people leave the green\yellow zones and tier 5 is enough to be able to do almost anything in the game effectively since thats when most spells are available. also tier 5 group dungeons seem to me to be appropriate achiavable maximum level of pve in the paddling pool (green\yellow) and 5.4 gear as appropriate wearable maximum tier for a person that has never left the paddling pool.
-make the difference in fame gained bigger between t5 and t6 (I think t4 and t7 are in the right spot probably). i think its best to lower t5 fame gained at the moment since people level too fast anyway
-make the fame gained dependant on the color of the zone same as gold. right now farming t5 yellow and t5 red is exactly the same fame wise and definitely not the same risk wise. same would apply to the difference between red and black zones.