Well coming from 3 R9 290X's and a 1440p FreeSync Acer monitor I will say I did not experience stuttering in the games I played (Though Rise of the Tomb did not like the 3rd card). The few games in the past I did experience stuttering on were fixed via AMD software updates but those were along time ago. I mostly played the Battlefield series, Tomb Raider (both of em), League of Legends, and some other random assortments of games temporarily and did not have the issue unless it was a game that specifically did not support CFX (Mostly some indie games or early DayZ and ARK). To me, on the 1440p 144hz setup with Freesync games were great especially my FPS's and League of Legends as that is where I game the most and I had 0 issues with them. I would recommend though getting the best single GPU you can get though before going CFX or SLI as both of the techs are good only when they work (Which for the most part all AAA games are pretty quick especially in this day and age to get that support). Personally speaking, I have tried both and to my eyes and experience they play out exactly the same (G-Sync vs Freesync 144hz 1440p in BF4 and 1 with multi-cards) and there really is no stutter in either of them. I would wait for Vega if you are set on replacing everything just to see what value comes with the new cards since it should be soon from the sound of things and then decide. The downside to investing in G-Sync is the price where as Freesync normally does not have (At least much) of an up charge. But to answer your question directly, no, if the game is going to stutter due to not working in SLI/CFX neither of the techs will fix that. It will however fix Vsync lag.