Spookie, the CEN site is a little confusing. In the spec box at the top it shows the manual for the esc. The manual has instructions for both the 80amp 4s esc and the 150amp 6s esc. But if you scroll down further on the product page it appears to show that both the Colossus and the GSTe come with the 80amp. Kinda confusing.

Yardman, I personally like higher voltage and the truck is certainly tough enough to take it. The only issue (besides the esc) with going 6s is you might have to change the gearing as well. It depends on how fast the truck is on 4s because 6s will raise the top speed and it might be too high causing the motor to overheat. Normally this isn't that big of a deal you drop a few teeth on the pinion or go with a larger spur. But I'm not sure if there is a larger spur available and the stock pinion is 12t. There are pinions as small as 8t-9t available (you'd probably want 9t on 6s) but pinions that small wear quicker. Sorry but I don't know all the specs on the Colossus to do any gear calculations to try and figure out if you'd need to change the gearing.