For starters, we wouldn't usually say
ma tasse de thé in French; usually we would say,
- C'est pas vraiment mon truc.
- C'est pas trop mon truc.
The nuance (at least in my area!) between the two sentences is not one of degree: they both mean the same thing as far as strength or emphasis is concerned. The nuance lies more in context.
I would tend to use
vraiment in a case where someone expected it to be my cup of tea, whereas I would tend to use
trop in a situation where I am in a discussion setting where there isn't really any expectation as to what my cup of tea is.
In other words, if my boss is asking me to do something that I really don't know how to do, I would tend more to use
vraiment, whereas if I'm talking with a friend about a particular activity, I might interject the latter expression.
They're synonymous. You can use them interchangeably. There is a slight nuance, however, as I outlined above.