Hi Paul,
Have you tried measuring some RV standard stars to calibrate your capability? The Soubiran et al catalogue prepared for Gaia gives a good list – https://www.aanda.org/articles/aa/abs/2013/04/aa20927-12/aa20927-12.html.
These are 6th to 10th mag stars and there are several dozen with RVs greater than 50km/s, both +ve and -ve. They are F, G and K type stars so good for using in cross-correlation. About 20% of them have southern Decs down to -10deg. This would let you see what consistency you can expect.
David