I can't get Dominiate to force a $5/$2 split, but I can tell it to buy Cache and Chapel on turns 1 and 2 if it does get the $5/$2 split, and play like Big Money in all other cases. (This strategy beats Big Money 54% of the time.) I can pair that strategy with a strategy that buys Chapel and Silver on a $5/$2 split, and plays big money in all other cases, and the former beats the latter 51% of the time.
So in Big Money decks, Chapel/Cache seems slightly better than Chapel/Silver. Bear in mind, though, that Chapel is not very good in Big Money, and Cache is. Conversely, of course, Chapel is quite helpful for many engines, while Cache is less likely to be. So in games with actual strategy, I still don't know if Chapel/Cache > Chapel/Silver or not.
EDIT: P.S., Big Smithy is improved by opening Cache/Nothing (rather than Smithy/Nothing) on a $5/$2 split. This is probably true for many Big-Money-plus-X strategies. Though not DoubleJack, it seems.