ARM vs x86

What software absolutely needs the x86 performance from the user and programmer  perspective? Why can't we switch to ARM even if it was ~4 times slower but much cheaper?

>>13
Ok. Implement following type-dispatcher, so it'll execute at the speed of C/C++ int addition

(defun add-fixnums (A B)
  (let* ((hash (or (shl (get-tag A) tag-bits) (get-tag B)))
         (h (aref handlers hash)))
    (funcall h A B)))