The 2 speakers in question are -
old: Infinity Primus P163 - used vertically as center channel
new: BIC FH6-LCR
BIC is 95dB vs 90dB, when I swap speakers without changing anything, its not really louder, and it should be if specs are accurate, correct?
Well the specs are not correct. I have done some careful checking.
Here is the problem.
I can find measurements of the primus series.
Now both speakers are specked by the manufacturers at 1 watt one meter sensitivity scale
However all the Primus series speakers are actually 4 ohm speakers not 8 as specified.
This speaker is virtually identical to your P163.
The speaker has pretty decent dispersion.
I can not find an impedance curve for the BIC. But assume it is 8 ohm then as measured by a sensitivity of 2.83 volts 1 meter, then the BIC would be 95 db sens, and the infinity 93 db, but the infinity would pull twice as much power from the receiver as the infinity.
Now add the fact that the BIC has a Horn tweeter and one that is likely to have much more on axis power and less dispersion it is easy to see how the speakers would have identical loudness with sensitivities quoted at 90 and 95 db 1 watt 1 meter.
The bottom line is that loudspeaker manufacturers specs mean virtually nothing unless you dig a lot more.