Anyone think 14g would be better?Yes, I do. Depending on which of the PSB speakers that are listed in your system description you would be using for surrounds it appears that their impedance is either 4 ohms nominal, or 6 ohms nominal and 4 ohms minimum. IMO, in general it would be good practice to keep speaker cable resistance to about 5% or less of speaker impedance, and preferably less. It can be calculated from this wire gauge table that the combined 100 foot length of two 50 foot conductors of 16 gauge copper wire has a resistance of about 0.4 ohms, or 10% of a 4 ohm speaker impedance. 14 gauge would reduce that to about 0.25 ohms, or about 6% of a 4 ohm speaker impedance. Still not ideal, but probably good enough.
Another issue that can arise when using long cables is inductance, which can result on upper treble rolloff and sluggish transients with some speakers. In this case, though, I suspect that the impedance of the speakers probably rises significantly in the upper part of the treble region, which together with the fact that you are just using them for surrounds will probably reduce that effect to insignificance.
Regards,
-- Al