Should I get the CR-10 or Prusa i3 and what upgrades ...
The Cr-10 will take a long time to heat up to high temperatures, 65 Celsius takes a couple minutes as is. The hotend would have to be upgraded with the Cr-10 if you plan to use materials hotter than 250 C, since cheaper hotends use a teflon tubing to cheapen down on machining costs.
Super hard nozzles - Test pilots - Page 2 - 3D Printing Forum
To be able to afford these for the research project, I started off with jewels intended for water jet cutting. They happen to come with suitable hole sizes, but then needs to be grinded into a volcano shape to be suitable for 3D-printing.