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Rechargeable cells are *designed* to charge at a rate equal to their capacity: the so called "1 C" rate. For example, 2A for a 2000 mAh capacity. I don't believe babying the charge at (0.1C or 0.2C) will increase lifetime but don't have a source to back that up at the moment.
Finding a definitive source is a problem. I looked before posting and found a lot of arguing and a few graphs. The consensus seems to be that .5A won't hurt battery life and 2A shortens it. But there's no agreement on where to draw the line between those two.
You're a bit off on the C rate for 18650 batteries. 1C is the nominal discharge rating. Thus a 3 Amp hour (3000mAh) battery can nominally provide 3 Amps of current for one hour. Although in reality the current will drop as the battery gets closet to fully discharged. 18650 spec recharge C ratings are all over the place, but typically in the .3 to .8 C range, meaning a suggested .9A - 2.4A charging current for a 3000mAh battery. But the battery manufacturers don't tell you if that's a straight safety spec or some tradeoff of safety and battery longevity. There's no actual standard.
Note that an x C rate doesn't actually mean the battery will get fully recharged in 1/x hours. As the battery gets to around 80% charged, the charge rate has to start dropping to avoid damaging the battery.
I admit I have more experience with lithium polymer chemistry (LiPo) than with lithium ion, the latter of which is what I believe most 18650s are. @lowwall, thanks for relating your more recent research.
Frustratingly, my XTAR charger wants to set the rate based on measured internal resistance, so it tops out at 0.5 A anyway for me. It's ready in the AM, so good enough in my book.