But those are beta drivers (whatever that means)
Here, it says the newes version is 301.42: http://www.geforce.com/drivers
That's irrelevant in this case. They are official betas. WHQL drivers have gone through the Windows Hardware Quality Labs testing. This, unfotunately, does not mean they are bug-free. Betas, can sometimes be more stable than WHQL drivers, and in fact that is the case here.
If you install betas, you will get a "Warning, these drivers have not passed the... Do you still want to proceed with the installation?" (something or other, can't remember the exact phrase). Just click OK to proceed. I can assure you as a Tom's gold medal "Addict", there is not a single thing to fear with beta drivers. If you still are unsure, then at least try out the 301.42 WHQL drivers.