PPM and SBUS are both protocols used to communicate between the flight controller and your receiver. PPM is an older protocol that has a delay of 18-27ms, and SBUS a newer protocol with features such as a different way to hand errors and a smoother and more accurate rc inputs, as well as a delay of 9ms.
Whilst this might not seem like much, it is the way cleanflight handles RC Inputs that makes the Delay more noticeable.
Cleanflight uses 3 point averaging, this means it takes the last 3 signals from the receiver and averages them out to create 1 signal. This helps it prevent signal frames from glitching.
This means that the delay is effectively tripled, so the PPM delay of 27ms goes to 81ms, and Sbus from 9ms to 27ms.
This is generally thought to be a noticeable difference by the community. Therefore we recommend buying an X4R-SB receiver over a D4R-ii. Since they are both priced the same by FrSky.
Installing an X4R-SB
Installation of the X4R is very easy if you have a flight controller with built in inversion, these include all F3 FCs as well as the Naze32 rev6. Simply wire in X4R to the 5v, Ground and UART RX Port.
For most F1 flight controllers such as the Naze32 Rev5 and CC3d. You have to invert the signal, so that the flight controller can read receive the information.
The easiest way to do is to buy an inversion cable, they can be found for around £3 on hobbyking.
However at drone insider we like to do the ‘A hole mod’. This means wiring the ‘A’ hole on the X4R to your white servo wire. And the Ground and Power to the regular 5v and ground pins. Here is a RCGroups article on the matter.
At the end of the day it is important to remeber that if your an average piolot and you have a naze rev 5 or CC3D which is working well with a D4R-II, there is no need to rush out and buy an X4R-SB, D4R-II is still a perfectly capable flight controller.