I told about DDC, CSP and also EHEIM. The MCP are "polyvalent" so their good results are as good for low restrictive blocks than for very restrictive blocks.
But in your post, you put a sort of "ranking", but this ranking could evolve depending of the type of block. The MCP are great and won't move, but for some blocks we are using in Europe (seems to be 50/50 between very restrictive and low restrictive block here) the EHEIM 1048 and the DDC (which is equivalent with EHEIM 1250 for the cascade in performances) will take better rank instead of the MD20 or others IWAKI pumps.
I just want to put in concept your ranking and not saying
Quote:
Recommended pumps:
Performance: Iwaki MD-20RZ
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in all cases.
For very restricitve blocks, I think DDC and MCP650 have a better "profil" than many powerful pump like the MD20.