So I was thinking of using them in on road usgt and stock17.5 would they work or would i need to go the 5?

Ec3 should be just fine for 17.5 but direct bullets to the battery would be better and have lower resistance which is ideal for 17.5. You don't really need it to handle a lot of power. Just needs to be as low resistance as you can manage.

+1

Direct line bullets also reduce weight (roughly 15-25g) which also lowers the center of gravity to improve performance. I always make it a point to reduce the wire lengths to the shortest length possible not only to reduce weight, but to also prevent the chance of reversing the polarity when hooking up the ESC to the battery