If you have a tablet as well, then limit the GTN to the critical stuff: ground speed, ETE to next waypoint, desired track, and actual track. You can put extra eye candy on the tablet if it's really important to you. If your vacuum system or even just the DG fails, you'll really appreciate having the track readout already up on the screen.
The other field that has the most potential safety value is GPS altitude, either on the tablet or on the GTN itself (replacing one of the track fields). Any other data fields on the GTN screen are a distraction, because too much information on display at once is as bad as -- or worse than -- too little (that's a mistake a lot of the newer avionics marketing material makes, trying to convince you that being distracted by a firehose of marginally-important extra data fields somehow makes you fly more safely; you need to be able to see the essentials in a glance, without having to waste a quarter of a second sorting them out from clutter).