Ideally I'd try to stay with plastic: I have no doubts that Pargu's wishbones will be strong enough, I think the concern is with the surrounding parts. I see the Optima Mid has a metal hanger (which will help a lot), but I can see you tear apart the front transmission casing instead.
3D printing may be an alternative: I'm using 3D printed arms on my FWD Buggy, and you're seeing it more and more - a nice example is JQ's 1/10 4WD Buggy, where pretty much everything plastic is 3D printed.
I also came across this thread (
link) - These seem like arms that were machined - or cut with a laser/water jet cutter and then had the holes cut in them. The result is a bit of a bulky looking arm, but they are in plastic and the fabrication of them is quite easy and might actually be the cheapest option.
If you're interested in the 3D printing or cutting options, please send me a PM, I may be able to help you out
Edit: It may also be worth checking if there are a few more of the Optima Mid arms available - I just found another link showing other machined arms from a different user! (
link)