Better to think about $ amounts than ratios for a TIRA. Your RMDs start around 4% at 70.5, so figure $4k taxable per $100k in TIRA. In addition, I would put in $50-$100k of medical/nursing/home care that you will probably be able to get out of a TIRA at 0% somewhere along the line. So for most folks, $150-300k is the minimum TIRA to shoot for, even if you only receive a 10% tax break.
But with 35+ years to retirement, things will/should change along the way. I hope you don't plan on being in the 10% bracket for another 35 years. You need to increase your income. As such, you will benefit more by doing a TIRA in the future when you can get 25-28% of immediate tax benefit and continue with the Roth-only for the time being.
Good Luck, -P
That is another good point and an idea that had briefly passed through my mind in the last couple days. I thought of it like this though: very roughly speaking I *may* have about 15,000 to 20,000 worth of deduction / expemptions in 2013 dollars that I could use the tIRA for. This (say 17,500) multiplied by 25 equals $437,500. Add in the 50-100k of medical expenses, which I hadn't thought of, and a good value of my tIRA could be (again, very roughly) $500,000 in 2013 dollars.
MGBGTV8 wrote: but we ARE planning many years in the future, with many opportunities for political risk to bite us!
Yes I am very very aware. Mostly, I just like to play with numbers and this exercise helps satisfy that. This at least gives me some kind of idea that there is a way to optimally use a tIRA while keeping taxes at or very near $0.00. Of course if life changes and I jump up tax brackets this will all change.