Try a good quality brace, I'm sure you'll be pleasantly surprised. When I made / fitted mine I wasn't expecting much, maybe a very subtle difference, but it was much more than I thought it would be. It was so good I almost immediately made a rear tower brace, which I was equally pleased with.
Having said that, if you're purchasing tailor made rather than rolling your own, I can't say that $X might not be better spent on say a stiffer rear ARB, but it certainly wouldn't be wasted on a good tower brace. Get both I say!
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