>If your tax rate will remain the same for withdraw as it does now, it doesn't really matter since the after tax value is the same whether you take out taxes now or later (i.e., tax_rate x (principal^gains) = (tax_rate x principal)^gains.
Assuming the money you invest goes up in value, aren't you better off in this scenario with a 401k over a Roth so that you can make gains on the money that would go toward taxes? You still have to pay taxes on the principal and the gains but compared to paying taxes on the money immediately, you're in effect borrowing money from the government at 0% to gamble with and keeping a portion of the return.
(Similarly, the expression tax_rate x (principal^gains) = (tax_rate x principal)^gains isn't true (beyond not being the right expression)).
.7 * (100000^1.07) != (.7 * 100000)^1.07 (assuming paying 30% in taxes and making 7% gains)