Penzance is like an incense that slowly changes flavors as the bowl progresses, sending the latakia to the back and the orientals forward and then slowly coming forward again during the smoke. No noticeable nicotine, just pure flavor, in a church, mass, monks Gregorian chanting and incense burning kind of way. Afterwards your pipes seems cleaner and happy.
Gaslight is a latakia bomb guitar driven explosions that goes off in your mouth with a dirty spray of smokey shrapnel, perique holes splattering your tongue, buzzing B bombers humming filling the air, whistles of latakia dropping carpet bombs of flavor across you tongue, BAM BAM BAM leaving your tongue exhausted and deforested and waving the white flag. The room note is that of burning cardboard. And, my pipes needs to be cleaned as it smells like the butt of a cheroot that was crushed out by a boot in the beer sodden floor of a dive that Mickey Rourke would look for prostitutes in.
Other than that, they are both tobaccos.