Some questions regarding the 6-8 bit models?

I had a few questions: I am getting a huge difference in performance when i load sd_xl_base_1.0_f16.ckpt vs sd_xl_base_1.0_q6p_q8p.ckpt. The codec in openStore is not set in both cased. The memory used is also the same in both cases. But when i load sd_xl_base_1.0_q6p_q8p, its much faster. Why is the case? I thought if i dont use any `codec` then it would just cast all the weights in fp16 format