how bad do I need new irons?
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I would say combine your playing this summer with some golf lessons. A distance fall-off after 7i indicates possible swing flaws. Lessons would be money better spent than getting new irons right away.
The Big Berthas are an excellent club for beginners - the clubhead and high-launch shaft get the ball up and flying.
And yes, be cautious of one launch-monitor session. Some monitors are more accurate than others. Beware of distance inflation!
If you get your swing stabilized with lessons, then you can switch irons over the winter. In the meantime, you can always test out different irons at demo days to see what you might like for the future.