From my experiance the mazell can be improved upon. I have one with 1/2 dittings and it has quite a bit of restriction. I swapped out a mazell for a gemini hi volume (3/8 fittings) and dropped temps 2 degrees(c) and greatly increased total flow.
Your heat exchanger is also a possible issue. But.....as you indicatd the flow is restricted, I would upgrade the waterblock first and see what that gets you. Then the heat exchanger if necessary (probably because of your pelt desire)
wj
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