Here's some info I found on front vs rear frequency....

"The rear ride frequency must be greater than the front. This is due to the fact that there is time delay between hitting an obstacle by front and rear wheels. The rule that the rear suspension should have a higher spring rate (higher ride or natural frequency) rationalized the observation that vehicle bounce is less annoying as a ride motion than pitch.
To minimize pitching tendency of vehicle one must plot the front vs rear ride frequencies in an amplitude vs time graph by considering the time lag. By performing various iterations of frequencies one can identify which two frequencies matches early so that there will be only bounce motion."

"One common idea is to design for “flat ride,” which is to have the rear suspension frequency roughly 15% stiffer (or faster) than the front. The idea is that since the front hits a bump before the rear, the rear should be a little stiffer in order to settle at the same time. Flat ride was initially designed to improve comfort on vehicles with soft dampers, but it’s also useful for sports cars. Many racecars do not use flat ride and there can be benefits to higher front frequencies. Ultimately, the best spring rates for a race car are the ones that allow it to go fastest around a track. This rarely comes from plugging numbers into a formula, but suspension frequencies and flat ride are useful starting points. Many variables are not accounted for with these methods, including sway bars and alignment settings."

"With equal or higher suspension frequency in the front, the pitching motion and out of phase front to rear motions will be more pronounced and the vehicle will have a tendency to pitch back and forth and not remain level after encountering some bump."