Fix downcasting for fp8_fast and add error to indicate you can't do scaled downcast currently

nodes_model_loading.py

@@ -1112,6 +1112,8 @@ class WanVideoModelLoader:
 
         if "scaled_fp8" in sd and "scaled" not in quantization:
             raise ValueError("The model is a scaled fp8 model, please set quantization to '_scaled'")
+        elif "scaled_fp8" not in sd and "scaled" in quantization:
+            raise ValueError("The model is not a scaled fp8 model, please disable '_scaled' in quantization")
 
         if "vace_blocks.0.after_proj.weight" in sd and not "patch_embedding.weight" in sd:
             raise ValueError("You are attempting to load a VACE module as a WanVideo model, instead you should use the vace_model input and matching T2V base model")
@@ -1465,9 +1467,9 @@ class WanVideoModelLoader:
                 if k.endswith(".scale_weight"):
                     scale_weights[k] = v.to(device, base_dtype)
 
-        if quantization == "fp8_e4m3fn":
+        if quantization in ["fp8_e4m3fn", "fp8_e4m3fn_fast"]:
             weight_dtype = torch.float8_e4m3fn
-        elif quantization == "fp8_e5m2":
+        elif quantization in ["fp8_e5m2", "fp8_e5m2_fast"]:
             weight_dtype = torch.float8_e5m2
         else:
             weight_dtype = base_dtype