* Volatile forint firms in line with emerging fx index * CEE investors are cautious ahead of key euro zone PMI figures * Warsaw stock index outperforms, partly driven by Santander stock By Sandor Peto BUDAPEST, April 17 (Reuters) – The forint set a new 3-week high against the euro on Wednesday, outperforming Central European peers as it benefited from increased appetite for emerging market currencies and stocks. MSCI’s indexes for emerging market stocks and currencies rose moderately as an unexpected recovery in China’s economy reduced fears of a global slowdown. Currencies in the European Union’s eastern states were mostly steady on investor caution ahead of key purchasing managers’ indexes (PMI) due on Thursday from the euro zone. Central European economies have lost some