Analysis of 861 participants over 17 years revealed that plasma protein GDF15 demonstrated the strongest association with mortality risk (hazard ratio 1.53), surpassing proteomic organ aging biomarkers for liver, immune system, and heart (hazard ratios 1.38-1.43). Among 202 mortality-associated proteins identified through comprehensive screening, CST3 and COL18A1 also showed robust predictive power. Established aging biomarkers including brain volume, cognitive function, and respiratory capacity maintained superior mortality prediction compared to newer proteomic organ ages. This comprehensive benchmarking study represents a significant advance in mortality prediction research, providing the first systematic comparison between emerging protein-based organ aging markers and validated multimodal biomarkers. The findings suggest that while organ-specific aging signatures offer valuable insights, individual plasma proteins like GDF15 may provide more practical clinical tools for mortality risk assessment. However, as this preprint awaits peer review, these results require validation before clinical implementation. The research reinforces that traditional measures of brain health and physical function remain gold standards, while highlighting promising protein biomarkers that could enhance personalized longevity assessments when combined with conventional aging indicators.