actually i'm not very sure what type of shots you are going after......maybe you can tell me more.
if you just want to have a collection of lens to cover wide field of photography and selling off your micro lens, go get the Tamron 17-50mm.
not point to get a sigma 24-85mm, trust me, if you don't like your 28-75, 24-85 will be the same. Unless you are using FF sensor and talking about 24-70f2.8 as a walkabout lens.
Image you sold off your 28-75mm and 60mm, getting a 24-85mm.
24-85mmf2.8-f4
50mmf1.8
80-200mmf2.8
or you prefer
17-50mmf2.8
50mmf1.8
80-200mmf2.8