The best replacement for m5 is m6.

The best alternatives to m5 are rated as following:
★★★★★  m6
★★★★★  m3
★★★★  e63
★★★  e55
★★  s6
★★  gtr
★★  rs4
★  cts-v
★  c4
★  550i
★  m6 gran coupe
★  rs6
★  911
★  tesla
★  c63
  mercedes e63
  panamera
  cts v
  rs7
  540i
  porsche 911
  s5
  z06
  s8
  r8
  e46 m3
  porsche
  amg
  e55 amg
  e60 m5
  isf
  e90 m3
  335
  audi rs6
  amg e55
  750
  10-32
  f430
  dunlop q2
  2006 e55
  x5m
  suunto quest
  audi s8
  jack3d
  porsche panamera turbo
  cls55
  550
  cadillac cts v
  535d

Your alternative for m5 is not listed? Suggest!
Speaking about m5, one probably shouldn't forget about no3.

Other search terms related to m5 and their ratings are:
★★★★★ no3
★★★ p6
You have in mind a companion for m5 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of m5 in all years. Click on graph for more.
m5
m6
m3