How to make prototype circuits that include microcontrollers, and avoid breadboard annoyances at high frequencies?
Fortunately, if you're using the internal clock, that 168MHz doesn't ever get to the breadboard.  Think of your max frequency as what's going on at the pins.

For that processor, though, the simplest way to go is to pick up the stm32f4 discovery board for about $15, and do your prototyping with that.  The useful pins are all broken out for you.

To get the signals you need from the Discovery board to something you can get at more is easy.  I like using 50-pin ribbon cable breakouts.  I use them to bring signals to breadboards, but they'll also bring them to solderable things like vectorboards.  The ribbon cable, of course, attaches directly to the Discovery board headers.

This is all intermediate steps, of course.  Eventually, when the bits and pieces of the design are all finished, you can print up a PCB with confidence, and move everything there.  If I may offer advice, though, a 100 pin package with 0.5mm pitch isn't necessarily the friendliest way to break into surface mounted devices.