Why you decided to buy front ARB at all? If you will upgrade both of ARB-s you will just make your car more uncomfortable for street driving and will not manage to reduce understeer at all. Eibach rear adjustable one is more than enough for our cars to reduce understeer. H&R springs + oem shocks on Sport+ mode are turning front end of our cars too stiff even for most of racing tracks, so I cant imagine how it feels on street.
There are a common rules on ARB-s:
To reduce body roll: Stiffen either or both bars
Reduce understeer/increase oversteer: Stiffen rear bar
Reduce oversteer/increase understeer: Stiffen front bar
In the wet: Soften both bars (possibly more off the rear to increase stability)
Do not go too stiff on the road, or on a very bumpy circuit. As usual, on the road less is often more, and on the track try a few setups, testing is king!
My car on track (pretty sharp corner) with oem ARB-s, shocks on Sport+ mode and H&R springs: