I have a gas leaf blower that requires 40:1 oil:gas mixture. I have a 1
gallon gas tank premixed with this oil gas.

I'm thinking of buying a chainsaw (stihl) which requires 50:1 mixture. Do I
need another gas tank to premix with this ratio, or is it ok to just use the
40:1 mix? Or perhaps I could put 45:1 mix in both??

BTW, all 2-cycle engine oil claim to be smoke-less. Which is the most
smokeless of all?