Continue as is if you are making good power. I have one racer in the Southeast who has a motor being run by an early DME which makes about 139 avg hp. He is also always in the top 4-5 with podium competitiveness in a field of 10+ racers at Road Atlanta.
The power is still there with the early DME, you just don't get the benefit of the extra 150 RPMs. I always shift at 6k so I rarely need the extra 150. I raced up until Watkins Glen (2016 Eastern Champs) on the late DME, which has the same rev limit as the early DME, and never saw an absolute need for the extra 150 RPM. In my experience, I am wasting RPM above 6k adding wear and tear to the engine and burning/blowing out more oil. My oil consumption each event went down when I started shifting at 6k rather than carrying my upshift to closer to redline.
You can source a late AFM for cheap ($40-80) and then purchase one of these new DMEs if you want the best parts, but it wont guarantee you will make more power.
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