My first post here so I hope I don't screw this up.
Depends on what you consider "good" loads. You can get good accurate ammo loading on a progressive press, but it will depend on a few things. Powder charge consistancy being huge. Powder choice will be huge for good consistant charges. There are things you can do to aid in consitant metering, but some powders do not play nice.
Get a Culver powder thrower, they are the most accurate. Sinclair has them.
For the best groups possible absolutely I would get a single stage and jam everything out single stage style.
Best press for this is the FOrster CoAx. because of the way it is set up, there is movement on the X/Y axis and allows the brass to index properly instead of potential concentricity issues that can happen with the "usual" single stages. The AMTU (which I tend to call the USMTU) has 20 of them.
A RCBS chargemaster combo or other good electronic powder measure/scale will greatly speed things up. You will get out of it what you put into it. Or if that is too slow look at a turret press. If you have more questions please let me know or shoot me a PM.
Lyman also has a superb electronic measure which also stores various loads.
Most of all, the reason single stage is best, is it allows for brass prep, like uniforming the primer pockets and flash holes (I do). Even on new brass (I'm using Lapua and Norma), it helps to make sure. I use one of Fred SInclair's original PP uniformers and a KM. Both work nicely and I know at least one other company that's working on one.
The Sinclair flash hole uniformer (P/N # 07-3081) is faster, but make sure to locktite the set screw. the flash hole diameter on the Sinclair is .081, the KM is .080. I haven't tried the others.
As for the "M" die. I use them mainly for pistol and rifle loads using cast bullets. You can use them to skip the chamferring step by just kissing the neck with the second step.
Also you can use a neck expander instead of reaming the inside of the neck. I use more than one depending on the bullet diameter. But I also trim to length and turn the outside of the case neck.
Hope this helps.