I am not sure about performance, but I do know you never replace one at a time, always replace in pairs or if the other wears out it will prematurely wear the new one and now you have to buy and replace three instead of two...

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1985 300D Turbo 332k Miles (daily driver)
1987 300SDL Turbo 320k Miles (needs new head)
1968 International Scout 800 V8 119k Miles (garage queen two years and counting)
2005 Kia Optima (backup car) 36k Miles (accident )