docs: tone down Phase 75-5 PGO recovery estimates

docs/analysis/PHASE75_4_FAST_PGO_REBASE_RESULTS.md

@@ -6,7 +6,7 @@
 
 **Key Finding**: C5+C6 inline slots optimization shows **+3.16% gain** on FAST PGO binary, meeting the ideal threshold but significantly lower than Standard's +5.41% gain.
 
-**Critical Concern**: FAST PGO baseline is **7.16% slower** than Standard baseline, suggesting potential PGO profile staleness or suboptimal training conditions.
+**Critical Concern**: FAST PGO baseline is **7.16% slower** than Standard baseline, suggesting potential PGO profile staleness, training mismatch, or build/layout drift.
 
 ---
 
@@ -155,7 +155,7 @@
 3. **⚠ Regenerate PGO Profile**
    - Train with C5=1, C6=1 (optimized config)
    - Use Phase 75 codebase for profiling
-   - Expected result: close gap to Standard baseline
+   - Expected result: uncertain; likely to improve if PGO was mismatched, but not guaranteed
 
 4. **⚠ Root Cause Analysis: 14% Regression**
    - Compare Phase 69 vs Phase 75-4 binary characteristics
@@ -176,7 +176,7 @@
 
 7. **Standard vs FAST PGO Convergence**
    - Investigate why Standard outperforms FAST PGO by 7-10%
-   - Consider unified build configuration
+   - Treat this as a measurement/forensics problem first (PGO profile, flags, link order), not an assumed “PGO must win” rule
    - Document PGO ROI vs complexity cost
 
 ---