A few comments from what I've read on this thread. It seems I read this stuff over and over and it's not clearly understood......

If you're a high earner, if all you care about is making tax free withdrawals when you retire (assuming you meet the requirements for the Roth withdrawal to be tax free), sure contribute to the Roth. Uncle Sugar is happy to have you pay higher taxes now then you might otherwise in the future. I don't get the fascination with the Roth. It's a tool in your financial toolbox. For some, it's a great tool. For others, not so great. Contributing to a Roth is not necessarily your best option unless you just enjoy paying taxes. If I was making $250K, I doubt I'd be contributing to a Roth unless I was going to be making a crapload of money in retirement or there was some extenuating circumstance.

If you get a lump sum of money and a large percentage is withheld, it doesn't mean you're paying that % in tax. The amount of tax you are going to pay is the sum of lines 45 and 46, shown on line 47 of your 1040. It doesn't matter if your employer withholds 100%, 0%, 25%, one dollar, or a million dollars. You go into the tax tables with the number on line 43, and that's the base tax you're going to owe (assuming no "other taxes" which applies to few). If a lot is withheld, you get a lot back or you owe less. If a little is withheld, you get less back (or owe more).

Contributing to a Roth 401K doesn't get you around the 415c limit. It's $52K for 2014. If you're 50 or older and you contribute to a 401k, you can exceed that 415c limit by the catch-up amount of $5,500.