I haven't come across any significant discussion surrounding this before and I wouldn't recommend choosing a machine on this basis.
A front-loading bobbin is only an advantage for changing mid-task if you catch it before the thread runs out, otherwise you'll be backtracking and starting again anyway once you've replaced it. I suppose if there is a viewing window and you can see when it is about to run out then this is an advantage, otherwise you won't know when to stop and change it anyway until you notice that it has already run out.
In terms of speed I doubt you will find any typical sewing machine "too slow" unless you plan to sew a lot and you want it finished quickly. For a few repairs or alterations and the occasional custom piece speed is not a priority, most of the time you will want to go slower anyway for more control/accuracy.
I think you need to put less thought into what machine you get and more thought into getting some machine and start sewing without thinking so much about details like how the bobbin is loaded. As a beginner these things don't matter, and by the time you are non-beginner enough for them to matter then you will know what aspects are important to you and if you want to upgrade. As it is, you can't really jump to making "expert-level" choices because you don't have the experience to know, for example, if speed is even a priority to you.