Early Retirement - 401k vs. Roth

[epollazzo]

I can never seem to get a straight answer.
I have two 401k accounts approx $100k each (1 from a previous employer). I am 38 and plan to retire early (hopefully) around 50-55. The 401k would be in penalty if I take distributions prior to 59 1/2, Should I convert my old 401k to a Roth? Am I correct that the 100K converted would be available without penalty at say age 50? What about if the account appreciated to $200k. Would it all be available penalty free? What about tax free? I am hoping yes and my Roth would bridge me till 59 1/2 where I can then start using my traditional 401k. Or am I just going to have to work until 70.
Any info would be appreciated...thanks in advance