Crap I totally forgot about the fact that output voltage is limited by input voltage…
You definitely want to go higher in voltage. When you only have one motor, you need to get as much power out of that motor as possible, and given that the ESC is limited to about 60-75A output, the 30% extra voltage will really help as long as you can fit the gearing to shift that power from high speed/low torque to low speed/high torque
Depending on your top speed goals, I think 12s is ideal for single 6374 builds. The size of the wheel limits the gearing you can achieve. On my 12s, single 6374 190 Kv build, I can fit 9:27 chain drive with 8mm ground clearance, for a theoretical top speed of roughly 25 mph. If I went down to 10s, I would lose power because the ESC limits prevents me from increasing current to compensate for the loss in voltage. If I went up to 13s without touching current, it would increase power, but I wouldn’t really be able to adjust the gearing at all, so all that extra power would just show up as more top speed (which I dont really need) instead of torque. And that’s at the expense of possibly reduced reliability and the extra cost of finding a (somewhat rare and expensive) 13s BMS and charger.
Also, consider LiPo packs. With 3p or 4p 30Q packs, you are getting 60-80A discharge which is plenty, but only 12-16A charge. A similar LiPo pack will get you closer to 25-40A charge rate for almost double the high-speed braking torque, which I think is a worthy consideration. It may have slightly worse longevity, but if you just undercharge by about 10% (which is a decent idea anyway to ensure you wont have braking cutouts at the start of your ride), you can help alleviate that.