How light does my hair have to be to get a light ash brown all over?

Hey, sorry I know this isn't exactly an "alternative" hair question.

Basically, I need to go back to natural colours for work and decided I wanted to try and go back to a light ash brown. My original hair was dyed a dark burgundy colour. A few days ago I used Colour B4 to remove any build up. Then I did a bleach bath. The roots took to it a lot better than the ends so now I have warm caramel coloured roots and medium brown tips. I plan to wait a week and do another bleach on just the tips (see first pic).

My question is, are my roots at a light enough level to get to a light ash brown? If not, what level would I need to get them and can you recommend either a box dye, semi-permanent dye and/or toner that would take it to a silvery ash brown like the second pic? Thanks.