Strength is not an issue with the 9 inch because all its flaws have been addressed with an aftermarket centre section and beefing up the case. $$$$ . Even a junkyard Dana will hold anything the average bracket car will throw at it. Even 8 second cars. Most guys will never swap ratios at the track. The s60 or a junkyard 60 is the cheapest way to a near bulletproof rear axle. Most bracket cars tax the rear axle at the trans brake hit. I have seen an 8 second dart using an 8 3/4 without failure because turbo cars don't launch very hard. I have also seen 11:50 cars (gas motor) with a Dana, that launch with the wheels 3 ft in the air. No one said either rear axle would et better.
If you have unlimited funds, and really might change centre sections at the track, go aftermarket 9 inch, buy 2-3 aftermarket centre sections and have at it. Or buy a new s60 and another ring and pinion and easily change gears. Ask yourself why you can now put Chevy 12 bolt gears in a 9 inch housing if there is no et to be had.