How much identity and fine-detail fidelity do 4-bit diffusion quantizations (SVDQuant, GGUF K-quants) lose, especially with LoRAs?

The SVDQuant paper reports 3.5x memory reduction and speedups for FLUX.1 and says it supports off-the-shelf LoRAs, while stable-diffusion.cpp and GGUF offer many quant types. No source here compares them head-to-head on face/character consistency, text rendering or LoRA stacking. Why this is still open: Reported metrics are authors' own and generic; there is no task-specific, independently reproduced character-consistency evaluation.