As was reported, the Steam Deck OLED comes with SteamOS 3.5 preinstalled, while the stable channel is still on 3.4.
This means if reviewers didn’t take care to properly match the software versions on the OLED and LCD models, they might not compare apples to apples. The effect is probably small, but so is the reported performance and power draw difference between the models. Also SteamOS 3.5 introduces the saturation slider which in its default setting tries to emulate sRGB more, and could affect screen comparisons.
See for example Taki Udon’s first video, where clearly it is visible that MangoHUD is an older version on the LCD model https://youtu.be/3C6ekDyO18s?t=807
So unless it is explicitly mentioned or shown otherwise, assume that part of the differences might be due to different software versions.
The power differences and performance are all based on changes in hardware. Do not expect an appreciable difference. Not to mention 3.5 is available to everyone here on the respective channel, and has been for a while.
tests are currently showing that the new chip is actually less efficient at lower wattages despite being 6nm
As another comment pointed out, the SMT bug is also fixed in 3.5.
The move to faster memory definitely helps performance, as was shown by those who overclocked the LPDDR5 on their launch models.
But the effect of both is game dependent, you can’t say it is all one or the other.