197 vs 200 arb

Go for the Cup Racer one.

The above statement is either incorrect or out of context. Either way it needs clarification.

If you are running stock suspension and you fit the cup racer one (or even the 1mm thicker 200 cup one) you will have understeer. 100% confirmed so the answer is no, do not bother.

Now if you are running a stiffer setup (like the 200 cup setup or stiffer) then going for the 200 cup will be beneficial yes. I wouldn't personally go for the racer one, too thick for a road car and needs to be coupled with super stiff setup which has the adverse handling effects on the roads anyway...
 
Stiffer front arb also reduces traction and as Yiannis says will make the car understeer more (when fitted in isolation). ARB's are used to fine tune when you're running a good setup, not before.