Play around with drivers - don't assume that the latest drivers are always the best.
When overclocking my 260 SLI system, until recently the most stable drivers were 197.13. Using any newer drivers than that caused flickering in multiple games, and some drivers gave me lower FPS with the overclock than when at stock. Luckily the last drivers that came out for my GPUs have been working very well, giving me perfect SLI support in GTA.. but this is the first time new drivers have helped me for months and months.
Play around with older drivers and see if you can get stable in them games. Or maybe if you're using older drivers already, try upgrading.
Besides that, I can't think of any reason them games should crash due to an overclock. I have MOH2010 myself and it works just fine with my cards at 720 instead of 576.