I used to have the Pilot III and have just moved onto the 96C. Both units are pretty much the same size, screen doesn't seem much bigger, but the resolution on the 96C is much better.
My main suggestions for what fields to use include using the "Next Waypoint Name" on the Map & HSI. No matter what other fields you use, without this you could be steering towards the wrong place! On the map page I use the Pointer, Time To Next, and Dist. The pointer is useful as an emergency brain dead guide should you become confused for any reason.
I mostly only fly with the HSI page as it allows for more accurate track control. You can perfrom an "OBS Set & Hold" as you approach your destination to input the Runway centerline. Couple this with the VNAV & you've got a mini ILS.
As for the 96C, my sugestion is that you will get much more for your money staying with the Pilot III. The 96C comes with a Yoke Mount which is OK but very bulky. The P3 is beter as it has a neat little screw on the back that allows you to make a simple mount to attach it to your kneeboard.
The 96C doesn't come with a carry case so add £13, It doesn't have an external aerial, so add £70, and doesn't come with a Serial Port cable, so add £23. (It does come with a USB connection but my version of Flitestar only works via the Serial port.)
So, I bought it for £445, and spent £106 on extras, plus postage and the total investment was around £580!! I sold my old Pilot III for around £220. Now I realize who got the better deal.
The features on the 96C are nothing special at all. The Obstacle alert facility doesn't seem to work in the UK as Jeppesen hasn't included them in the database. The "Select Approach" function which allows navigation to the FAF & MAP on published instrument approaches souds useful, but is actually quite confusing. The waypoint management system requires too much button pressing and feels disorganized.
The good points about the 96C are that its COLOUR and that it only uses only 2 x AA batteries which last much much longer than the Pilot III. The 96C comes with a nice software program which allows you to download your flight history. The Pilot III has this facility via Flitestar, but the 96C is much better as it not only displays the Track, but also Height, Speed, Times and can be displayed as a profile (altitude X-section) so you can monitor the accuracy of your climbs & descents.
So, stay with the Pilot III if you can, but if you want to upgrade to the 96 series get the 96C over the greyscale 96 otherwise you won't notice the difference and feel ripped off!!