Dennis,
The "C" factor roughly correlates to the internal resistance (R
int) of the particular cell. The higher the "C", the lower the internal resistance--at least if the "C" factor is set by the physical characteristics of the cell rather than the marketing department!
So where all this matters is in the heating of the pack during use due to the resistive heating (I
2R
int--a real killer of packs.
Another thing to remember, flying at partial throttle is harder on a pack than you might suspect. For example if your throttle is set at 70% of full, then your average current "I" is being supplied only during 70% of the time. Or in other words, the peak current I
peak is actually 1/.7 (~142%) higher than the average current (I
ave)you measure. So the heat produced in the pack during the "on" time is 1.42
2 or~ 2 times what you would calculate from using I
ave. However the other 30% of the time the pack is supplying nothing, so when you take the average of the on and off periods, you end up with 1.42 times what you would calculate from using the I
ave for the heating calculation. So you see you may be a bit harder on the pack than you think.
But cutting through all that --are your packs hot when they come out of the plane after a flight? If they are just "warm" then I don't think you are over-abusing them due to heating.
So getting back to your first question, heating is bad, so a "real" higher C rating is better. But the other thing to remember is that most high "C" rated packs are heavier than the lower "C" rated packs (I am thinking about my 18C FMA 2100 mAHr cells and the Thunderpower Lite cells too). Sometimes it seems like if you would just buy a higher capacity but lower C rated cell, the the allowable amps out is basically the same as the lower capacity but High C cell---and both have roughly the same weight. (I haven't made any precise determination of this, it is just a feeling).
There are also issues (just look at the battery forum on RC Groups to see the controversy) about whether the super cheap packs are really capable of many cycles (since initial cost/(# flights) gives the real cost of a pack). I know that some people are measuring some of the new packs like Hyperion and Thunderpower (both ~35C or higher and not "cheap") are capable of realistic 10C type use (a 6 minute flight) for >200 cycles before a loss of capacity is noted. Of course they are only discharged to the 80% level for each cycle.