What a particular connector is safe to use at what voltage and amperage... is a highly debated and discussed subject. The fact are that they depend on how much the load is, how long the load is applied... what voltages and amperages ( as mentioned ) we are talking about and even the gauge and length of wire that is used. The makers of the Deans connectors, never would rate their connectors for the reason that more than just the connector must be considered. I think they didn't want to state a rating because they wanted to limit their liability and placed that responsibility on the user to ensure what they used worked in the situation they were being used in.
I had chose to use the larger Deans since it was a commonly used one at the club I was at allowing us to swap batteries easier... and because most if not all of my planes used 40a or less at 3s and 4s voltages. I probably wouldn't be too concerned using those connectors with up to 60a loads but I read a lot of folks really pushing it and going up to 100a. I strongly suspect the ones going up to 100a were only do that for very short bursts and weren't using them at anything close to a constant load.
With an airplane, it's relatively easy to get an amperage reading safely, I'm uncertain if there is a similar way on a heli. If there isn't, I'd use worse case estimates like the max rating for the ESC as a starting place then add an additional 10-25% more for a safety overhead amount. Then pick a connector that gives you at least that amount of rating. I'd follow up with manually checking the temps of the connector and wires after a hard flight to help verify that you'd estimated on the safe side.
Quoting Wikipedia on the melting point of solder for info on that...
Soft solder typically has a melting point range of 90 to 450 °C (190 to 840 °F; 360 to 720 K), and is commonly used in electronics, plumbing, and sheet metal work. Alloys that melt between 180 and 190 °C (360 and 370 °F; 450 and 460 K) are the most commonly used.
Based on that... I don't think the problem to worry about is going to be the melting of the solder but the failure of the connector or wire. In short, the plastics used will likely soften sooner cause a potential failure much sooner than the solder would melt. Of course the high temp silicone covered wires that is used on the higher quality parts is also a pretty high temp... so I'd probably worry most about the connector plastics the most. These reasons are why I'd worry about the cheap knockoff brands that many buy just because of cost... don't be a penny wise and pound foolish.
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