just_updated_compare.rb

require 'benchmark/ips'

Benchmark.ips do |x|
  x.iterations = 10

  x.report("just_updated") do
    Version.just_updated(50).to_a
  end

  x.report("just_updated_new") do
    Version.just_updated_new(50).to_a
  end

  x.compare!
end

out.sh

$ rails runner lib/just_updated_comapre.rb 
Warming up --------------------------------------
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
        just_updated     1.000  i/100ms
    just_updated_new     1.000  i/100ms
Calculating -------------------------------------
        just_updated      1.155  (_ 0.0%) i/s -      6.000  in   5.192876s
    just_updated_new      9.744  (_ 0.0%) i/s -     49.000  in   5.028857s
        just_updated      1.180  (_ 0.0%) i/s -      6.000  in   5.086182s
    just_updated_new      9.751  (_ 0.0%) i/s -     49.000  in   5.025749s
        just_updated      1.174  (_ 0.0%) i/s -      6.000  in   5.110814s
    just_updated_new      9.781  (_ 0.0%) i/s -     49.000  in   5.010069s
        just_updated      1.172  (_ 0.0%) i/s -      6.000  in   5.118410s
    just_updated_new      9.658  (_ 0.0%) i/s -     49.000  in   5.078506s
        just_updated      1.171  (_ 0.0%) i/s -      6.000  in   5.122628s
    just_updated_new      9.759  (_ 0.0%) i/s -     49.000  in   5.020966s
        just_updated      1.171  (_ 0.0%) i/s -      6.000  in   5.121990s
    just_updated_new      9.762  (_ 0.0%) i/s -     49.000  in   5.019853s
        just_updated      1.177  (_ 0.0%) i/s -      6.000  in   5.098674s
    just_updated_new      9.770  (_ 0.0%) i/s -     49.000  in   5.015508s
        just_updated      1.189  (_ 0.0%) i/s -      6.000  in   5.044222s
    just_updated_new      9.784  (_ 0.0%) i/s -     49.000  in   5.008067s
        just_updated      1.187  (_ 0.0%) i/s -      6.000  in   5.053813s
    just_updated_new      9.779  (_ 0.0%) i/s -     49.000  in   5.010926s
        just_updated      1.176  (_ 0.0%) i/s -      6.000  in   5.100921s
    just_updated_new      9.759  (_ 0.0%) i/s -     49.000  in   5.021151s

Comparison:
    just_updated_new:        9.8 i/s
        just_updated:        1.2 i/s - 8.30x  (_ 0.00) slower