Not sure about your data. Lyman CBH 3rd ed shows the following
Lyman 245496 at 83 GR Lyman #2 in 243 Winchester
Start load 8.5 grains 700X at 1684 fps.
Consider that significant reduction, large case, possible stuck bullet. I not think that much of a reduction prudent. Maybe start backing off from the start load in .2 grain steps to find where results are erratic. Then increase back to reliable grouping. Keeping in mind this will be a summer only load and cold weather will change results.