The problem isn't with the wheel coming apart, the problem lies in the exponential increase in torsional stress on the spindle. All of the failures I've seen pictures of started with the shaft snapping.
Yes, a HEALTHY 7M-GTE long block can withstand 400-450 (other things will need to be beefed up, of course). But, if you're going to go to all the trouble build for more... it'll last a lot longer.
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