The best replacement for 2.4 is 5ghz.

The best alternatives to 2.4 are rated as following:
★★★★★  5ghz
★★★★  2.6 ghz
★★★  5.8
★★  5
★★  5 ghz
★★  5.8 ghz
★★  2.6 macbook pro retina
★★  5g
★★  1.8 ohm
★  2.6
★  2.66
★  2.8 macbook pro
★  5 gigahertz
★  2.5 ghz
★  5ghz band
★  5 ghz wireless
★  5.0 ghz
★  5ghz speed
★  5.8 phone
★  5 wifi
★  2.8 ghz
★  5.8 fpv
★  5.8 cordless phone
★  5ghz wireless
  2.5 macbook pro
  5ghz router
  5 wireless band
  pentium 2.4
  2.53 ghz
  5.0 ghz wireless
  2.2
  900
  2.7 toyota
  2.66 ghz macbook pro
  2.7 tacoma
  5 wireless n
  5.8 ghz phones
  5.8 ghz phone
  5 wireless
  5.8 gigahertz
  5 ghz range
  5.8 mhz
  2.53 macbook pro
  5.8 wifi
  2.2 defender
  2.6 linux

Your alternative for 2.4 is not listed? Suggest!
Speaking about 2.4, one probably shouldn't forget about php 5.3.

Other search terms related to 2.4 and their ratings are:
★★★★★ php 5.3
★★★ php 5.2
★ php 5.5
You have in mind a companion for 2.4 and it is not yet here? Propose!



Google Trends

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2.4
5ghz
2.6 ghz