Mild overclocking is totally safe as long as you keep the temps below dangerous levels (for the most part, under 90C is acceptable.) In most cases it's a bit dumb if you aren't overclocking, since that's free performance you're missing out on. Worst case scenario if you push the clocks too far, you will experience an ASIC hang and the GPU will freeze until the system is rebooted.
Yes there is a GPU stress test tool -- it's called oclHashcat
There's also md5stress (see the wiki.)
Edit: By the way with a GTX 970 you can probably safely do +225 - +250 clock offset.
Yes there is a GPU stress test tool -- it's called oclHashcat
There's also md5stress (see the wiki.)Edit: By the way with a GTX 970 you can probably safely do +225 - +250 clock offset.