How to correctly isolate sense lines, and drivers, and coax cables, and noisy environments
None of the above mitigates differences in ground noises which degrades the SNR.
If your noise is induced into the buffer, which only needs to be to a GBW say twice your requirement.
The termination must be differential across 50 Ohms if the noise is being induced on the 50 Ohm Cable. This can be tested simply with a 50 ohm source replacing the buffered signal to see what your noise pollution is on the cable before you see how much is getting in to validate your assumption.  A series of CM chokes must be added to the Coax or simply use the 20MHz filter on the DSO unless saturation occurs on the CM signal.
Each connection from one ground to the next by cable needs a Pi filter with CM choke and caps to local ground. I suggest 1kOhm @ 100MHz DCR=1
Clam-shell CM chokes are inductive over 1 to 2 decades in frequency , so more than one of different spans may be needed on the sensor cable.
The cost of clamshell beads varies from about US$0.50 to US$10.00each depending on the source.  Smaller coax can be wound several turns to raise the CM impedance. Then RF shunt caps to ground will increase CM attenuation greatly while limiting differential impedance by chosen limit. &gt;= 20MHz
Some well-known manufacturers of ferrite beads are:
Manufacturers
Fair-Rite Products Corp. http://www.fair-rite.com/newfair/index.htm
Ferrishield   http://www.ferrishield.com/
Ferroxcube    http://www.ferroxcube.com/
Murata        http://www.murata.com/products/emc/index.html
NEC/Tokin     http://www.nec-tokin.com/english/product/dl_emc.html
Parker Chomerics  http://www.chomerics.com/products/emi/cableconnector.html
Laird (Steward) http://www.lairdtech.com/Products/EMI-Solutions/Ferrite-Products/
TDK           http://www.tdk.com/ferrites.php
Würth Electronik   http://www.we-online.com/web/en/passive_bauelemente_standard/willkommen_pbs/Welcome.php