I saw a comment by 'dvs-626' about making a sticky post about proven mods or proven 'fails' to save people time and/or from making the same mistakes. Great idea I think
Max voltage on the cars
Somewhere between 4.8V and 6V, 4.8 is safe, 6 will kill it. That's all you need to know as far as 1.2 and 1.5 multiples go, when I start playing with a variable voltage I will be able to narrow that down a bit more.
Feel free to reply here with other suggestions and I will add to this first post as we go