I dunno, man. A Cache/Chapel opening gives you a much higher chance of T5 Chapel Syndrome than any other $5 card --
Chapel/anything else = 2/12 = 17%
Chapel/Cache = 4/14 = 29%
That's 12% of games, one in every nine, that you just lose because of this opening, that Cache better be totally off-the-wall, bonkers-sauce, amaze-balls, rock star, super hero to be worth it.
But it's Cache, man. Chapel mitigates the awfulness of it, but if you want a Chapel, you want those Coppers gone yesterday and now you have two more of them to clean up, at best you're losing a turn of pace, that Gold better be worth it, man. That Gold better be so much better, like super-way-mega-ultra better, than any other card costing $5 or less that you are willing to assume all of this risk and loss of pace to get it in your deck before you have it under control.
COuncilroom would seem to concur http://councilroom.com/openings?card=Cache
A better statistic to look at might be this:
http://councilroom.com/openings?card=Chapel63 single Kingdom cards (I didn't count Nomad Camp/Chapel/Fool's Gold, it requires quite a bit of stuff to happen and it made my calculations harder) had better openings, and this was pre-Dark Ages, so there were only like 157 total cards available. That means the odds of there being no better option than Cache to open with your Chapel are roughly ((157-63)/157)^8 = 1.7% (OK this is just an upper bound but it helps make my point). I doubt that you could really apply this statistic very well to an actual game of Dominion, though.