I'm not sure exactly what you mean by implementation here, but many (most?) of the Wikidata examples (on its public endpoint) are very fast, i.e.: https://query

I'm not sure exactly what you mean by implementation here, but many (most?) of the Wikidata examples (on its public endpoint) are very fast, i.e.: https://query.wikidata.org/#%23Cats%0ASELECT%20%3Fitem%20%3FitemLabel%20%0AWHERE%20%0A%7B%0A%20%20%3Fitem%20wdt%3AP31%20wd%3AQ146.%0A%20%20SERVICE%20wikibase%3Alabel%20%7B%20bd%3AserviceParam%20wikibase%3Alanguage%20%22%5BAUTO_LANGUAGE%5D%2Cen%22.%20%7D%0A%7D https://query.wikidata.org/#%23Cats%0ASELECT%20%3Fitem%20%3F...