16GB DIMMs in 2010 Mac Pro
It can run 64GB as dual channel [8's] or 96GB as triple [16s].

From EveryMac - Silver-Colored Mac Pro Q&amp;A


  Actual Maximum RAM
  
  Although "Mid-2010" and "Mid-2012" Mac Pro systems with a single
  processor, which EveryMac.com notes as the "Quad Core" and "Six Core"
  models, officially support a maximum of 16 GB of RAM, as discovered by
  site sponsor Other World Computing, they actually can support more.
  OWC first noted an actual maximum of 32 GB of RAM and later increased
  this actual maximum to 48 GB of RAM.
  
  Systems with dual processors, which EveryMac.com notes as the "Eight
  Core" and "Twelve Core" models, likewise officially support 32 GB of
  RAM, but again, OWC found they actually can support more. OWC first
  confirmed an actual maximum of 64 GB of RAM running Mac OS X 10.5
  "Leopard" and later increased this maximum to 96 GB of RAM running Mac
  OS X 10.6 "Snow Leopard" or higher. More recently, OWC yet again
  discovered these dual processor models can support up to 128 GB, but
  only when running a 64-bit version of Windows XP or later or Linux.
  Mac OS X only can support 96 GB of RAM.