That might be your charge pump limited bandwidth, but the loop
filter would reduce it from there. I'd expect by at least 10X for a
decent phase noise (you have to flatten the pump ripple).
I'm no PLL expert but find it odd that there is no AC term in
your bandwidth equation. You'd think the capacitance on
the charge pump node would be fundamentally limiting.
Now, if you broke the linear single-pole paradigm (say, with
a loop amp that had dual slope, one for near-null and one
for high-error that slews harder, maybe you could realize
a better net bandwidth (if bandwidth is aimed at a frequency-
agile application and not for optimizing some frequency-
static attribute).