VSOP, the pears you refer to do sound like great pears. I don’t have direct experience with any of those. I have no reason to criticize Cummings. I will add that my experience with Just Fruits and Exotics has been excellent.
I do believe that Magness has a reputation for being a pollen sterile variety. By the way Ayers has a similar reputation. Consequently if you get three trees be careful that the other two are effective polinizers of each other and Magness. There is reasonable doubt that Magness and Warren might actually be the same variety in which case it may also be pollen sterile. Golden Boy is not gritty. Southern Bartlett is very soft. It’s more melting but the texture is not as fine grained as Golden Boy. VSOP, I would love to add any of the above you mention to my orchard if I had the space to do it.
Something to consider when planting pear trees is the range of uses you have for the pears when you get them. A situation I may face in a few year is an overabundance of soft pears with a short shelf life. Something to consider is choosing three varieties with multiple application and / or with good storage qualities. You may detest a course grained pear when eaten fresh, but would you really prefer a soft pear cooked or canned over one that is firm? Carnes and Baldwin are two pears for example that have reputations for being fairly fine textures but firm. For fresh eating, I prefer the soft, super sweet and juicy pears. But five years from now when I have pears coming out my ears, I might end up wishing a larger percentage of my trees produced firm pears suitable for a broader range of processing uses. God bless.
Marcus