I am selecting some speakers and I would like to mix a vintage 30 with a G12K-100. The vintage 30 has a sensitivity rating of 100 compared to the g12k-100's rating of 99

Becasue I don't know nought about this scale and all I can find on the web is 'make sure the difference isn't too big'.

What is too big?

Time on earth is like butterscotch; you really want more, even though it will probably just make you ill.

Certified lurker
The vintage 30 will be 1dB louder. 1dB is the smallest difference in volume detectable by the human ear.
Gear List:
Ibanez S320
Lavey LV200
Squier Stratocaster Affinity HSS
No-Name Wesley Fat Strat copy
Peavey Rage 158