I've had a standard dash and now a NISMO LCD dash in my 33, and while the tacho is accurate, the speedo is slightly out (I think that might be the wheels I'm running tho, or possibly another factor), the fuel gauge is good enough, and the water temp gauge is not accurate at all. I love my GReddy water temp gauge, its sooo handy and you dont realise how inaccurate the factory gauge is until you have an aftermarket one.
It also saved my motor yesterday when I popped a coolant bypass hose. Noticed it was running hotter then normal and was able to pull over and shut it off before I did any damage. The stock gauge hadnt even moved
Hope that helps! Thats my personal experience anyway