Flex mode RAM loss only matters above 16GB.

You won’t notice it in normal use. The performance hit only kicks in when your workload exceeds the dual-channel portion of your total RAM.

In your example – 8GB soldered + 16GB replaceable – the first 16GB run in dual-channel. That covers most games, browsing, Office, even light video editing. The remaining 8GB on the 16GB stick run single-channel, but you only hit that if you’re maxing out 16GB.

Benchmarks show 5–15% slower memory performance in that overflow zone. For stuff like rendering, heavy VMs, or huge data sets, sure, it matters. For everything else? You are not going to feel it.

If you are worried, check your actual memory usage. Task Manager or Activity Monitor will tell you if you ever cross that 16GB line. Most people don’t.