All Gunslingers should be using the internal proc relic. The energy/kinetic proc relics require the presence of substantial amounts of global armor penetration to be valuable. Sharpshooter doesn't get any global armor penetration (it gets a single instance of specific armor penetration to Aim Shot, and not even all that much).
Keep in mind, the differences between choosing the proper DG proc relic and the "wrong" DG proc relic (as long as you're getting a DPS relic), is single digit changes in total DPS. When you're already pushing 1.9-2k DPS, you're probably not going to notice any difference in whether you're using the correct DG relic, especially since the natural variation in your DPS thanks to lag, variations in skill and reaction speed, etc. are all going to make a *way* bigger difference.
Just as a comment on this, my artifice can craft the Kinetic Tempest relic, which I made for a Gunslinger in my raid group. He did an ops dummy parse and we looked at the log details.
Grav Wave is the proc attack from the relic, and it was hitting for 204 non-crit damage with Flourish Shot up (mitigated down from 280 damage), as compared to the 210 damage he would have gotten with the Internal relic.
As Kitru says, the difference is minimal.
Edit: As I recall (it's been a while) my Commando was getting 238 damage per non-crit Grav Wave, due to the additional armor penetration.