These relics are beaten with a wide gap (stat & effect wise) by any endgame relic which none of them has alignment requirements.
For the record it is always ok to RP your characters, and will likely make the game far more interesting than choosing LS or DS based off of what you normally choose. It's especially fun to be neutral on a class like BH or IA. My BH was mostly LS but it was fun as hell to punch out mouthy nobles on alderaan during my class quests.
To OP: My first character was a SI(sorc healer) and I have to say, if you want to lightside I would do SI in an instant. There is a very beautiful ending(or segment of the ending) that can only be achieved by an LS sith. I wont spoil it for you, but im sure you can look it up on youtube.