1 dyno

$ ab -c 100 -t 60 http://pure-depths-6229.herokuapp.com/ 
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking pure-depths-6229.herokuapp.com (be patient)
Completed 5000 requests
Completed 10000 requests
Completed 15000 requests
Completed 20000 requests
Completed 25000 requests
Completed 30000 requests
Completed 35000 requests
Completed 40000 requests
Completed 45000 requests
Completed 50000 requests
Finished 50000 requests


Server Software:        gevent/0.13
Server Hostname:        pure-depths-6229.herokuapp.com
Server Port:            80

Document Path:          /
Document Length:        12 bytes

Concurrency Level:      100
Time taken for tests:   19.182 seconds
Complete requests:      50000
Failed requests:        0
Write errors:           0
Total transferred:      8200000 bytes
HTML transferred:       600000 bytes
Requests per second:    2606.61 [#/sec] (mean)
Time per request:       38.364 [ms] (mean)
Time per request:       0.384 [ms] (mean, across all concurrent requests)
Transfer rate:          417.46 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        1    2  26.9      1    3010
Processing:     4   36  53.0     28    1326
Waiting:        4   36  53.0     28    1326
Total:          5   38  59.3     29    3036

Percentage of the requests served within a certain time (ms)
  50%     29
  66%     32
  75%     35
  80%     37
  90%     46
  95%     69
  98%    132
  99%    307
 100%   3036 (longest request)

50 dynos

$ ab -c 500 -t 60 http://pure-depths-6229.herokuapp.com/ 
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking pure-depths-6229.herokuapp.com (be patient)
Completed 5000 requests
Completed 10000 requests
Completed 15000 requests
Completed 20000 requests
Completed 25000 requests
Completed 30000 requests
Completed 35000 requests
Completed 40000 requests
Completed 45000 requests
Completed 50000 requests
Finished 50000 requests


Server Software:        gevent/0.13
Server Hostname:        pure-depths-6229.herokuapp.com
Server Port:            80

Document Path:          /
Document Length:        12 bytes

Concurrency Level:      500
Time taken for tests:   17.181 seconds
Complete requests:      50000
Failed requests:        10
   (Connect: 0, Receive: 0, Length: 10, Exceptions: 0)
Write errors:           0
Total transferred:      8198360 bytes
HTML transferred:       599880 bytes
Requests per second:    2910.13 [#/sec] (mean)
Time per request:       171.814 [ms] (mean)
Time per request:       0.344 [ms] (mean, across all concurrent requests)
Transfer rate:          465.98 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        3   74 436.1     15    9042
Processing:    13   85 104.8     49    1800
Waiting:        0   85 104.8     49    1800
Total:         26  159 448.6     65    9297

Percentage of the requests served within a certain time (ms)
  50%     65
  66%     78
  75%     99
  80%    122
  90%    196
  95%    390
  98%    962
  99%   3068
 100%   9297 (longest request)

server.py

from gevent.wsgi import WSGIServer
import gevent.monkey
import os

gevent.monkey.patch_all()


def application(environ, start_response):
    status = '200 OK'

    headers = [
        ('Content-Type', 'text/html')
    ]

    start_response(status, headers)
    return ['Hello World!']

WSGIServer(('', int(os.environ.get('PORT', 8000))), application).serve_forever()