Aiming at highly reliable microprocessor soft error tolerance design, a new metric, eMWTF (enhanced mean work to failure), was proposed to capture the trade-off among reliability, performance, area and power. A quantitative approach for evaluating eMWTF was also presented. Two control flow checking techniques were quantitatively evaluated in reliability. The experimental results indicate that the control flow checking by compiler signatures and hardware checking achieves better trade-off among reliability, performance, area and power. Because the eMWTF metric takes into consideration performance, area and power overheads, the quantitative reliability evaluation can be more accurate by using this metric and corresponding methodology. Finally, the evaluation results can effectively guild the design exploring and optimization.