Pattern steering arms seem to all be in the range of 25-30pound each.

Genuine ones are about 100pound each.

So you could use three copies for every genuine one. The question is do the real ones last three times as long under the race conditions you're going to subject them to? Also, what is the cost of having one fail? Does that mean rebuilding the car after it's hit something?
Same question applies to the strengthened steering arm. What is the chance and cost of failure of a standard one? Does the cars intended use justify the uprated arms?
Most importantly, how deep are your pockets?