Your GRE quant score is good to show schools. But to me, it says absolutely nothing about how you would do in higher math.
My advice is to take some harder math/physics classes and see how you like them.
For starters, something along the lines of...
1) Differential Equations (ordinary and partial)
2) Complex Analysis
3) Probability (calculus/measure theoretic based)
4) Linear Algebra (I would not even consider this to be advanced, but as you didn't say you had taken it, I went ahead and listed it)
And if you want to get fancy...
1) Real analysis
2) Stochastic Calculus
3) Quantum Mechanics
4) Lagrangian Mechanics
As it happens, these are also the right classes to have under your belt going into an MFE.
Cheers.