::Browsing the web, the 6000 ft/min figure is widely quoted. There are many articles that say the flight recorder data won't be included in the preliminary report (which hasn't been publicly released). Again, the graphic comes from a presentation given by the Transportation Minister. 
 ::However, I forgot to point out that the graphic comes from radar data (from the aircraft's transponder), not the flight recorder (although this conflicts with earlier statements that radar contact was lost at 23:17 or 23:18). Perhaps there is a discrepancy between what the transponder reported and what was recorded by the flight recorder. I don't have any knowledge of exactly what the FDR records, but it's quite likely that the FDR records the position based on GPS and that this is what was used to provide the 6000 ft/min rate. I also don't understand how variable the pressure altitude can be compared with the actual altitude, but considering that they were flying into a storm, the outside pressure may have varied relatively significantly, causing a large and/or highly variable difference between the actual altitude and pressure altitude (flight level sent by the transponder). While doubtful, the design of the altimeter/barometer could also contribute to the discrepancy between actual and pressure altitudes. This isn't an attempt to get off-topic and start a forum-like discussion, but rather an attempt to explain the difference.  
 ::I think the best thing to do for now is leave the values in the article, since they come from reliable sources and we don't want to introduce original research, but could insert a footnote after the climb rate about the discrepancy.