Plus, with @Voxel's firmware, you might have a way to tweak/boost the wifi signal from terminal access and scripts.You have nothing to lose. You can try voxel fw and go back to ddwrt if it does not meet your requirement of signal strength. Boosting signal strength than the optimal range may also increase signal to noise ratio. 2.4 GHz band has more coverage, smart lights can be connected to 2.4 band only. R7800 is pretty good in terms of coverage, though depends on various factors like router placement, house construction (concrete walls), competing wifi channels (use some web analyzer to see other channels in your area) ...
Ddwrt gives more options to tweak in the ui. But it is missing the hardware NAT acceleration. It may not be a concern if primary priority is smart lights but if performance/speed is the main priority it makes a difference.
Second thing is stability, voxel's fw has top notch stability. Many folks restart the router at next fw update with voxel's fw. May require few tweaks to adjust to one's environment/location like adjusting congestion control ... but once you know what works best for you, performance and stability remains same weeks after the fw install/update.
You will know what you are missing (if anything) after trying it for few days.
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