There's a lot of factors involved... price the harv sells for, how long it takes to harvest, the time it takes to walk from storage/NPC and back, harvest events slowing the process...
So with my 760 EMU, I decided to run some tests on some popular items that are harvested to sell. Worst case, I'd have some extra stock of the items. ;)
Items normally sold to NPC (Lupies, lilacs, titanium) used the NPC price, others used a sell-to-user price based on what harvest shops on the EL forums normally charge, which is close to if not the normal selling price anyway.
I did a minimum of 3 full loads for each item, counted how many of the item I got and how much time it took including full walk back/forth to storage/NPC. These were "perfect" conditions, meaning the harving was monitored to restart the harv as soon as an event stopped it, started the walk back to the harv/sto/NPC as quickly as possible, etc.
Note that your experiences may differ! How much EMU you have could easily affect which item is better. Less emu = more trips, therefore if the trip is a considerable part of the time involved, you might end up making more money with a harv that has a shorter walk. These calculations are based on an EMU of 760, with excavator cape. (My harv level is 86 as well.) Other factors, such as your AFK time, amount of events, broke all your tools and had to return early, etc., should also be kept in mind. And of course, the price you actually sell the item for. (Personally, I'd be stubborn as a mule and refuse to sell for less than the given prices below.)
So when it came to best gc per hour, here were the results (NPC/Player sales separated because NPC you get gc directly, sales to players do not include the time it takes to actually make the sale, just the time to collect it in storage):
Sell to NPC (instant gc gratification)
Titanium ore (WV @ 2.5ea) - 3420gc/hr
29Lilacs (VotD @ 0.5ea) - 2916gc/hr
Sell to Players (delayed gratification, wait for large amount sale)
gypsum (Arius @ 10ea) - 8640gc/hr
iron ore (EVTR @ 3.5ea) - 6552gc/hr
sapphires (PL @ 3.2ea) - 4838gc/hr
sulfur (EVTR @ 2ea) - 4680gc/hr
emeralds (EVTR @ 3ea) - 4536gc/hr
blue quartz (NC @ 2ea) - 4464gc/hr (rose/regular quartz in NC about the same)
diamonds (Irin @ 3.2ea) - 4032gc/hr
silver (MM @ 2ea) - 3672gc/hr
henbane (SRM @ 2ea) - 3096gc/hr
turquoise (glac-2-AAsto @ 5ea) - 3060gc/hr
wormwood (SRM @ 2ea) - 2880gc/hr
toadies (VotD @ 1.5ea) - 2646gc/hr*
(* Toadies note: Problem is slow harving combined with low sale price, not the trip to storage, so using SRM won't really improve this by much. This is an item that should have been moved up to the 2gc price range with other higher-level flowers, but due to its use as food, people will refuse to buy it at higher than 1.5.)
The results: If not in a rush, iron is the true champion. However, there's some boneheads out there who regularly try to buy it for less. Don't sell to them, ever. If you sell for 3gc each instead of 3.5, you'll be better off selling Lupies to the NPC. Seriously.
Why not gypsum? There are some out there willing to buy it. Mostly potioners making extracts. It will likely only sell in lower-thousand amounts though due to price and potioner need, and the number of people who'd need it is very limited. As well, the big problem with it is the walk from it to storage and back, being a lot of time and clicking spent on that, with very little time on actual mining. It's a pain in the ass, and is the primary cause of the high cost. Being the heaviest harvable is really a secondary reason to the trouble of harving it.
Iron on the other hand has pretty much guaranteed buyers, in huge amounts, at any given time.
If you need the money as quickly as possible, and don't want to have to deal with finding a buyer, Lupies are the way to go for NPC sales.
Notes: Give the item weight consideration. Heavier (like iron) will mean more trips. If you prefer to afk-harv, a lighter item might be better for you in the long run. Don't forget the harv experience you get for each item, weigh that in your considerations if you are looking to advance your harv level at the same time. Lupies are obviously a poor choice for that, heh.
