Competition Better Valves

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Is there a need for better, stronger valves when running about 4800-5200rpm? I have seen alot of failures with the stock cummins valves in industrial engines and was wondering if upgrading to a stainless steel, inconel valve would be well worth the extra money. I can either have both valves made at 1. 77 (same as intake but larger than stock exhaust) or have both made at stock size. Is there any big advantage to going . 120 larger on the exhaust valve?