Any Topre keyboard you get will be a lot quieter than a model M...the comparison isn't even close.
If you're planning on using it for gaming, definitely look at a uniform as the variable will be annoying. If you rest your hands on the keys a lot, you'll also find the light keys very annoying...but as far as comfort is concerned, the variable does make a lot of sense for typing...It is a lot more noticeable when you go back to a uniform topre from a variable and can feel how much harder you need to work.
But that said, you're on a M right now so you won't miss what you don't know..and the uniform ones will feel a bit more familiar with a keyboard that will already feel different to what you're used to.
I'm not sure going down to a 60% is the right move for people right away..they look cool..but really it does take a bit of an adjustment...If I were to pick one keyboard that I'm going to be using all the time for any situation and using it a lot, I don't think it would be my HHKB...I really like it, it feels great, it works great, it looks cool, it is really convenient for a lot of different situations..but would I be happy with it for everything? Probably not...
I think most people suggesting 55g Topre for you are probably spot on considering you're coming from a model M..but 45g is, IMO, a bit more comfortable...Unless you really slam your keys hard, they'll still be very tactile...but definitely a lot lighter than what you're used to at the moment and that may throw you off...