The threat of soft error induced system failure in high performance computing systems has become more prominent, as we adopt ultra-deep submicron process technologies. In this paper, we propose two techniques, namely soft error mitigation (SEM) and soft and timing error mitigation (STEM), for protecting combinational logic blocks from soft errors. Our first technique (SEM), based on distributed and temporal voting of three registers, unloads the soft error detection overhead from the critical path of the systems. Our second technique (STEM) adds timing error detection capability to guarantee reliable execution in aggressively clocked designs that enhance system performance by operating beyond worst-case clock frequency. We also present a specialized low overhead clock generation scheme that ably supports our proposed techniques. Timing annotated gate level simulations, using 45 nm libraries, of a pipelined adder-multiplier and DLX processor show that both our techniques achieve near 100% fault coverage. For DLX processor, even under severe fault injection campaigns, SEM achieves an average performance improvement of 26.58% over a conventional triple modular redundancy voter based soft error mitigation scheme, while STEM outperforms SEM by 27.42%.