I doubt that it is a guarantee that it t would break but I know Marlin Crawler has a strong preference for having the 4.70 gears in the rear case in a dual ultimate setup.
The real question is why you think going that low is necessary? I also run the dual ultimate gearing and can't see a real value for lower gearing. If you truly do have a need then do it right. If not then don't waste the money.
The reason BigMike runs triples is that having the 2.28 gears is valuable and you'd be eliminating seversl useful gear ranges by only having 4.7 and 4.7 x 4.7.
2.28 and 2.28 x 4.7 are of far more practical use than 4.7 x 4.7 will ever be.
