Where has my bandwidth gone?
To not leave this question without an answer, here's the solution that I commented earlier:
My first suspicion would be the incredibly large 1.6kOhm resistors (and the 4.7kOhm ones even more, of course). You just need 2pF of stray capacitance to get a -3dB rolloff frequency of 60MHz with a 1.6k resistor. If you want to go to such high frequencies, all resistors in the signal path should be on the order of at most 100 - 200 Ohms.
Of course, you have to be careful to not go too low with the resistance, otherwise power dissipation will get out of hand and/or your buffers won't be able to drive the low resistances properly.
Really nice to see that this solved your problem!