I commend you for wanting to avoid an unnecessary biopsy - there certainly is a rush to biopsy in the US. However, you have done your due diligence and you can't rule out a high probability that you have prostate cancer.
4Kscore is a better test than PSA alone or free PSA - it includes both and adds two other biomarkers. It has been validated for all PSA values (not just 4-10). In fact, more than a third of the men in the validation study (below) had a PSA under 4. Among men with 4Kscores in the 10-15% range, 40% had prostate cancer discovered on biopsy. OPKO recommends that any 4Kscore over 7.5% be a trigger for a biopsy./www.prostatehealthuk.com/media/1411-4Kscore-US-Clinical-Trial-Eur-Urol-2014.pdf
The drop in total PSA may indicate that there is some prostatitis, but because you have high risk of prostate cancer, I'd think you'd want a biopsy.