So I started with 16:8 about 6 months ago. A few months in I would push it a few more hours to 18:6 or 20:4 sometimes. These days I do a mix of OMAD, OMAD+, and 16:8. My weight loss has been more or less the same throughout, a nice constant 2-ish lbs a week.
It really still just comes down to the calories you consume. If that extra two hours helps you eat less it might help, but it’s not going to suddenly be twice as effective or anything. There’s also health reasons for not wanting to go too fast. The recommended rate for weight loss is 1-2 lbs a week, or 1% body weight.
If you want to give it a try go for it, but you’re doing good work with 16:8 so far too.
I’ll do 18:6 if I’m not hungry or if I got busy and forgot to eat. I haven’t noticed any extra weight loss though since I try to plan my meals out ahead of time. I’m not consuming fewer calories. The one reason I try to do 18hr or longer is in the hopes that it has skin benefits through autophagy.