Only 3 wheels are confirmed the be PS4 compatible; the T500RS, the upcoming T300RS, and the one everyone should ignore, the T80 Driveclub edition. I say ignore it as it is a bungee cord wheel rather than a proper (re: REAL) FFB wheel. TH8RS or TH8A shifter sold separately however.
If your willing to spend the money, the $550 (Depending on where you get yours, mine cost me $530, but $550 is about average.) T500RS is the most optimized wheel for GT6. You can save you some bucks with a brand-new Logitech G27 for just $300 straight from Logitech. With that, you get a shifter and a clutch pedal.