Cpus lifespan is well in excess of 20 years. For most ppl who tend to keep a pc longer than the 'gotta have latest and greatest' freaks, will undoubtably run into the Real judge of a cpu's lifespan, Software. A perfect example is my (yes it still works!) Intel Pentium II 350MHz (OC to 400MHz) that's 20 years old. Runs Windows 98SE with 1Gb of ram and a 16Mb 3dfx Voodoo gpu (AGP slot). It can't run XP or better OS. It can't run Minecraft. It can't be upgraded. Software demands on clock speeds, ipc, ram have made my old pc as obsolete as the hand cranked old jalopy.
3800MHz across all cores, under safe limit voltages and temps won't even put a dent in the software lifespan. Your pc will be as obsolete as my old PII long before it dies from electromigration. 4.2GHz at 1.4v+ and constant 90°C+ temps would be a totally different story.