I just completed my promotion to Rear Admiral. The Corvette looks nice parked next to my Cutter. I don't own an Anaconda, never have... that's for peasant trash to travel about in.
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You can try 17 Draconis. I ran dry for me, and I had to do the last 2 ranks purely at TUN. The last rank ( Post Captain to Rear Admiral ) ran 4 delivery missions to 1%. Previous ranks were not that bad, maybe 3.5 or so per 1% for Post commander to Post Captain. I tried every other place.
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Ceos/Sothis : There were not enough Fed factions there to make it worth your time. Mode switching helped, but it took longer to get to the magic 20 data delivery missions between Ceos and Sothis. Just doing the short data delivery missions was pretty lucrative and I made loads of money, but not much rank.
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17 Draconis : While the donation missions were there, it certainly speeded things up. But they ran dry ( for me, at any rate ). I was able to pick up 7-10 per mode switch, and that was limiting myself to 200k and under at the start. Then, 'poof', and it was maybe 1 or 2. I had loads of cash ( billions, in fact ), but it wasn't worth the time and mode switching for 1 or 2 missions. There weren't many delivery missions, since it's pretty much in the middle of no-where. It's donations or nothing, and once I did the time versus rank percentage gained math...
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Taribes : Better than the last two systems, but the delivery ranges were a bit far. An Asp outfitted as an explorer makes this a bit better as long as you have some shields. Lots of missions, but one or two jumps between them took more time than... Tun.
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Tun : It was miserable. Hated every second. I ran ( by my numbers ) over 700 missions out of that port. I made decent money, but spent it on every donation mission I could find, even the 1 million credit ones. The only saving grace, was that by the end I knew my 'route', and would hit the mission board on every system picking up delivery missions for other systems on the route. I got 7-10% per complete run this way. About 2 weeks, spending 3 hours a night, for my last two ranks. That was as efficient and 'fast' as I could get it. I would have GLADLY spent 200 million credits at 17 Draconis to avoid that last rank.
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All that being said ( or typed ), I don't believe there is such a thing as 'fast' ranking any more. Unless maybe 17 Draconis starts handing out donation missions again. It also seemed to me, that the mission board didn't refresh like it did several weeks ago. Private group and Open were usually identical so mode switching didn't help there. Solo was always different. BUT, it seemed that there was no way to force a refresh of the board with all new missions in Solo or Private/Open. I even tried completely logging out and starting the game from my PC's desktop. The only thing that seemed to work was waiting for the 10 minute timer to expire while waiting at the main menu. Then you could re-log, mode switch Solo/Private/Open, exit to the main menu, and wait out the 10 minute timer again. Time spent waiting for this to happen greatly affected my 3 hours a night.
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Doing the low levels, Ensign and below should be fairly quick at Tun. But, as most things in ED, the closer you get to the top, the harder it is. 400 missions for the last rank seems excessive, and it is. You should also note that if you aspire to a Corvette/Cutter, that grind is just the first step. Both those ships will EASILY run you north of 500 million credits to outfit, and that doesn't not include engineers mods. So rank will get you NOTHING if you don't have a billion in the bank.