First, I recommend posting this in the Sim Hardware section, not here. Second, a lot of people do use Fanatec wheels, in fact I would say they are extremely popular with CSP being the best pedals and with their new releases.
What I can tell you though is the G27 is a huge step up from the DFP and DFGT. The FFB is better and much smoother. Having an H-gate shifter is a huge plus for those who use it. The paddles have a great feel to them, very positive feedback when shifting. The buttons on the wheel are nice but I grew used to te DFP placement and have difficulty at times with what is where.
The pedals are a huge upgrade, the difference is amazing. This us what will decrease your lap times the most. Threshold breaking is so much easier and you can be a lot more consistent. I NIXIM modded mine and they feel awesome, especially for only $35.
How much time did it save? I guess it depends on the track but for me on a track like La Sarthe in a 787B it was around 2+ seconds. Others it may be just a tenth or two. I do WRS mainly so I'm rarely on a car track combo for more than a week so it's hard for me to answer.
Edit: Why did you create a second thread here when daan just redirected you and closed your other one?