I run an RTX 3060 Ti which works great with MSFS. There's no need for DLSS since I only run at 1080p, but it's a brilliant piece of tech for upscaling to higher resolutions.
The performance of DLSS basically scales with the actual (non-upscaled) resolution. For example, with Balanced, you get the same performance at 4K as you would get at 2227x1253p without DLSS. Performance mode at 4K = 1920x1080p and so on. There's a tiny bit of overhead for the actual Deep Learning upscale, but in reality it's barely noticeable.
While you might see MSFS fill up all available VRAM regardless of whether you have 6, 8 or 12 GB, in reality it doesn't necessarily need all that VRAM. It's just taking advantage of all VRAM since it's there to use.