as hell vs only too

as hell

adv
  • To a great extent or degree; very. 

  • 2004, Teralee E. M. Bird, Seraphim Trilogy Book One; What the Herald Angel Sang 

  • Even though he was frightened for them, even though he was scared as hell to fail them, it felt so good to know these people cared when he hurt! 

only too

adv
  • to a high degree; very well or very much 

  • very, all too. 

How often have the words as hell and only too occurred in a corpus of books? (source: Google Ngram Viewer )