Kingmeow
Quarry Creeper
@Kingmeow
Thanks for all the details. I was more lost than I thought!
So now that I think I get what's going on, I can NOT charge two full sized packs with a parallel board on my Thunder AC6.
If I want to charge (two) 4000mAh packs at 1C (4.0 amps), I would need 59.2 watts, but my charger's max output is 50 watts.
Perfect! You get the idea here. You can still charge them with your AC6 even though it puts out max 50 watts and you want 59.2 watts out of it. It'll just reduce the charge current so it'll take slightly longer to charge (59W and not that far off from 50W).
It would, however, work on my 1.7mAh packs because 1C would only be 1.7 watts.
I think you mean 1700 mAh which means at 1C it's 1.7A, not watts.

So, with my smaller crawler packs i could potentially charge 4 at once at almost 1C.
Right?
Also, if I did want to charge all four, would it take about the same time as charging just one because the charger would simply output more wattage?
Correct. Four of your 2S 1700 mAh at 1C, charges parallel will need 50.32 watts (4 x 12.58). Pretty much at the limit of your 50 watt charger. Yes, it would take the same time as charging one pack.
I also want to make you aware of something else that *may* further limit you due to your charger's specification. Hopefully this won't confuse you more.

Let's take your 2S 1700 mAh pack as an example. Charging four will need 50 watts, which your AC6 can handle since it's 50 watts max. BUT, your charging current needed is 4 x 1.7A = 6.8A. And assuming your max current is 6A, the charger will scale back to 6A since you reached that limit and not the 50 watts limit first. You need to check the spec of your AC6.
For my Revolectrix GT1000, it's 1000 watts with a max charge current of 40A. Yeah, it can charge big packs in parallel with no problem.

EDIT:
Looks like the AC6 can only do max 5A. So since your really need 6.8A in the above example to charge at 1C, you will charge at a lesser current of 5A, less than 1C, thus your charge time will take longer. BUT, it will still be quicker than if you charge one pack at a time.
https://www.hobbypartz.com/thac6smbachw.html