Off scalp or on scalp bleach?

Hi guys. I'm now blonde again. Right now my hair's the shade of medium blonde with a tinge of orange which is nearly unnoticeable in the back. Now, I'd like to go blonder, to a light ash blonde that isn't quite platinum. I'm not aiming for platinum blonde but a very light blonde shade on cool side.

I'm wondering if off scalp bleach works better, say, Manic Panic Flash Lightning or should I stick to something like 7th Stage or Wella Wellite? I noticed that 7th Stage takes longer to go lighter while Wellite pretty much lifted me to a level 9 pretty quickly. After all I'm probably going lighter by 1 or 2 levels or shades in addition to doing my dark roots which lighten in less than 30 minutes. Which one is more gentle?

I'd like to use Born Blonde Blissfully Blonde or Silent Snow. I'm not sure about Wella ColorCharm Silver Lady, which is quite silvery but ashy on yellow hair.

Ah...just read the box...it is indeed off scalp.  Damn, that means I have to grow out my roots for a while too