context: been doing a little grinding for some of the current records, used livesplit and it seems that either livesplit itself runs at a faster speed than the IGT timer by a difference of -+2s, varys between devices lil' bit weird

Just tested it and Livesplit running faster than IGT is probably normal; my game runs about 59.5 seconds IGT per RTA minute (so 4:00 IGT corresponds to 4:02 RTA). My games UPS was stable at 30 for this test, did not drop to 29 at all; I suspect the UPS is rounded and the actual UPS was stable around 29.75. This would also explain why you see different numbers between devices.

CHLEFF's Ruins Repurposed run has the same effect and around the same numbers as me (5.50 IGT ~ 7.71 RTA -> 36.70 IGT ~ 39.12 RTA) would correspond to about 0.4 second difference per minute of gameplay.

Are your numbers relatively consistent with the above?

yep, the longer the run went on the more the range increased from IGT which would keep in line with your above message