Using stash search you can look for items that are higher or lower in item level, requirement level or quality. It will draw an outline around items that match the pattern.
Use 3 designated keywords to describe your search pattern.
ilvl:nn - where nnn is any 1 2 or 3 digit number
rlvl:nn - same deal for required level
qual +nn - where nn can be any 1 or 2 digit number
Use hotkeys to change whether to search higher or lower.
, (comma) search for lower values
. (period) search for higher value