we ended up climbing at 4000+fpm well ABOVE the intruder, so missing him was plain luck. In the debrief the IP confirmed, that this was the very correct reaction.
GPWS takes priority over RAs, but I was told that below a certain ( radio Alt ? ) altitude descent RAs will be inhibited .In your case you maneuvered against the RA and that puts the odd of having a collision extremely high. Especially if the intruder was also TCAs equipped.( and logically had also a climb RA ) Going back to previous altitude (after the GPWS)was probably the safest option , assuming the intruder was TCAS equipped and followed his climb RA. If the intruder was Mode C only , you cannot win that situation .
All this in theory and with 20/20 hindsight of course...