Just wanted to clarify, is it true that with seatpost setback and saddle pushed backwards one will be working out his glutes more, compared to zero setback and saddle forward will be working out quads more? Which is the stronger muscle and more effective for speed

Strength is rarely a limiter for cycling performance.

Yep. It's usually groupset or stem angle

And stiffness.

No, it's bike weight.

Yes, more or less.

The glutes are theoretically the strongest muscle group, but sitting disease causes them to fall asleep.

More effective for speed? What kind of twitches you favor, & what you've trained for I suppose...

Yes to question 1. Question 2 is more complicated. In general, for endurance riding the more muscles you use, the longer you last. For speed work this doesn't seem to be true, possibly because coordination speed is a limiter. While some say that strength is a limiter, ever look at the legs of an elite track sprinter? They look nothing like the legs of a grand tour climber. So it depends on what you want to do. The principle of specificity applies: you get better at what you train to do. IOW your question is too general.

Havent started training yet at all, just got the cycling bug not so long ago. Thus i am looking to focus on working out the right muscles henceforth. Find it hard to sustain a constant 25mph, therefore wondering if its easier to train up the quads or glutes to achieve that and keep up in group rides

Riding more will get you there faster than training specific muscles.

Also, if we're talking about sustaining 25mph while riding on your own, well, good luck with that.

pretty easy when you "average 23 mph for 40 miles"

especially if upgrading to deeper dish wheels that "hold speed better"

Oh, right...

For someone with those abilities, focusing on the glutes is definitely better. The ladies will want to suck that wheel all day to enjoy the view.

NA. You need to train up your aerobic system. Muscles don't have so much to do with it. Ride a lot, especially hills. Keep track of your weekly mileage. Increase it by no more than 10%/week. Ride 80% moderate, 20% really hard. It is said that most riders ride neither easy enough nor hard enough. It takes time, but progress will be noticeable in about a month. Don't overdo it. If you legs say they don't want to, don't, go easy instead.

I aim for the seat position that doesn't cause my knees to hurt. YMMV

Wow thanks! Will report back after a month on the improvement (if any)

Bike color, of course...