This thread is about button top batteries for a Provari power device.
To answer your question, the vtc6 is 3000mah, the vtc5a is 2500mah, you might notice a slight gain in runtime with 3000mah cells.
Of course that is dependent on your power devices low voltage cutoff.
Higher low voltage cutoff (3.2v+) 3000mah, lower low voltage cutoff ( - 3.2v) vtc5a.
If for some reason I wanted to vape a 2 cell power device at 120w I'd use 25a CDR cells - vtc5a or LGHD series, at 100w or less - Samsung 30q, vtc6, LGHG2.