why artifacts: in cores containing disabled pipelines/cache/shading units etc., which are usually bridled down versions of 'better' models, those hidden features are untested. Or, the core itself was tested as being unsuitable for the higher model and was then scaled down by disabling faulty parts.
Depending on demand, you can have plenty good cores sold as low versions - those are the best to unlock because there's a high chance of a perfect feature unlock without artifacts - or mainly cores that failed the higher level tests and were sold as lower capabilities units - those either have faulty behaviours, or those can't scale up well in higher frequency.
The best way to know is to try, and Rivatuner being a software-only unlocker, you have nothing to fear trying it.