Easy question to answer for Midge, he's got plenty of padding & will stay rugless until it gets really cold & wet and he loses some weight. Obviously I will be monitoring him, and will put his New Zealand on before he loses too much weight, but that won't be for a while.
Alfie is not so easy. He is out at night in an old middleweight New Zealand at the moment, buy he has a very fine coat. This last weekend he turned rather fluffy. Unlike the gentleman of leisure, Midge, Alfie is in work and does get quite sweaty. Well he does when anyone other than me rides him, I'm still trying to keep my balance so we mostly walk, with very short bits of trot and canter.
So Alfie may need clipping soon. He probably won't have a rug change yet. Though he may start to wear his Snuggy Hoods turn out good after clipping.
Once he's clipped he will have a cooler or fleece on in the stable during the day, and as the temperature drops we will consider either rug or routine change. While the ground is fairly dry he will stay out at night. When it gets wet and muddy, he'll come in and go out during the day.
I'm not a fan of single heavy rugs, particularly for horses stabled overnight. I prefer layers, so I can be more subtle with temperature control. The girls at Talland would say Alfie is spoiled with his wardrobe, much of which he inherited from his predecessor.
One brilliant tip I got from a client is keep two good, waterproof lightweight rugs, and use them as the outer layer, no matter what you use underneath out in the field. The idea meant I never had to remove a horrible, wet, muddy rug. The lightweight, which was easy to hose off, got muddy & we didn't have to try to deal with wet middle weights. With drying rugs really hard on that yard this made a huge difference.
Check out other people's ideas on Autumn wardrobes for their horses