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Steel springs are run below their fatigue limit, but only became really reliable after shot-peening became common. That was the secret of Toledo swords, too, BTW. Anyway, if you were to have your springs etched down, you could get any strength you want, and the loss of the surface treatment would probably be compensated by the reduction in strain, if the change is substantial. Springs, valve train weight, RPM and lobe shape all interact. The reduced duration on an XFI cam gives it a peakier lobe, even with less lift, so the need for spring strength is not reduced along with the power band. If you are willing to be religious about a low red-line, there are definite gains available, though.
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