DAC80004: Max Sample Rate / Update Rate

Tool/software:

Hi,

According to datasheet the DAC80004 Update rate is limited to 200Ksps and the DAC80504 is up to 1Msps,

these two parts have the same architecture R-2R, and SPI Clock speed of 50Mhz and a similar settling time,

I'm trying to figure out what are the key parameters that makes the max update rate difference which is is very different while the above parameters are quite the same,

((is it small signal transition architecture that makes the difference or something like that?)

Thanks in advance,

Barak