Asymmetric dual channel beats single channel for gaming.

Add the 8GB stick. For most games, having proper dual-channel memory matters more than having a few extra gigs of capacity. The first 8GB of your 12GB will run in dual-channel mode (4GB soldered + 4GB from the 8GB stick), and only the leftover 4GB falls back to single-channel. That’s a net win for frame rates and consistency.

Sure, if you’re playing a game that slurps up 14GB+ of RAM (city builders, some open-world titles), the single-channel 16GB setup might keep you out of swap hell. But for 90% of gaming, the performance advantage of dual-channel outweighs the capacity difference. I’d take 12GB dual-channel over 16GB single-channel any day.

If you know you play RAM-hungry games and can live with slightly choppier performance in return for not hitting the page file, go the other way. Otherwise, keep the 8GB stick.