Here is how a simple "Hello World !" compares between LUA-Turbo/D-Vibe.d:

LUA ==memory 10.2MB = complexit 3/10 == Requests per second: 54042.70 [#/sec] (mean)
D ==memory 17.6MB = complexit 7/10 == Requests per second: 30355.65 [#/sec] (mean)

----LUA
local turbo = require "turbo"

local message = "Hello World!"
local header = turbo.httputil.HTTPHeaders()
header:add("Content-Length", tostring(message:len()))
header:add("Connection", "Keep-Alive")
header:setstatuscode(200)
header:set_version("HTTP/1.1")

local hdrmsg = header:stringifyasresponse()
local buf = hdr
msg .. "\r\n" .. message

local function handle_request(request)

-- This is the callback function for HTTPServer.
-- It will be called with a HTTPRequest class instance for every request
-- issued to the server.
request:write(buf)
request:finish()

end

-- Assign callback when creating HTTPServer.
local httpserver = turbo.httpserver.HTTPServer(handlerequest)
http_server:listen(8888)
turbo.ioloop.instance():start()

----D
import vibe.appmain;
import vibe.http.server;

void handleRequest(HTTPServerRequest req, HTTPServerResponse res)
{

if (req.path == "/")
	res.writeBody("Hello, World!", "text/plain");

}

shared static this()
{

auto settings = new HTTPServerSettings;
//settings.options |= HTTPServerOption.distribute;
settings.port = 8086;
//settings.bindAddresses = ["::1", "127.0.0.1"];

listenHTTP(settings, &handleRequest);

}

~ $ ab -n 500000 -c 500 -k http://127.0.0.1:8888/
This is ApacheBench, Version 2.3 <$Revision: 1604373 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 127.0.0.1 (be patient)
Completed 50000 requests
Completed 100000 requests
Completed 150000 requests
Completed 200000 requests
Completed 250000 requests
Completed 300000 requests
Completed 350000 requests
Completed 400000 requests
Completed 450000 requests
Completed 500000 requests
Finished 500000 requests

Server Software:
Server Hostname: 127.0.0.1
Server Port: 8888

Document Path: /
Document Length: 12 bytes

Concurrency Level: 500
Time taken for tests: 9.252 seconds
Complete requests: 500000
Failed requests: 0
Keep-Alive requests: 500000
Total transferred: 56000000 bytes
HTML transferred: 6000000 bytes
Requests per second: 54042.70 [#/sec] (mean)
Time per request: 9.252 [ms] (mean)
Time per request: 0.019 [ms] (mean, across all concurrent requests)
Transfer rate: 5910.92 [Kbytes/sec] received

Connection Times (ms)

  min  mean[+/-sd] median   max

Connect: 0 0 0.2 0 7
Processing: 3 9 1.2 10 24
Waiting: 3 9 1.2 10 24
Total: 6 9 1.2 10 24

Percentage of the requests served within a certain time (ms)
50% 10
66% 10
75% 10
80% 10
90% 10
95% 10
98% 11
99% 13
100% 24 (longest request)

~ $ ab -n 500000 -c 500 -k http://127.0.0.1:8086/
This is ApacheBench, Version 2.3 <$Revision: 1604373 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking 127.0.0.1 (be patient)
Completed 50000 requests
Completed 100000 requests
Completed 150000 requests
Completed 200000 requests
Completed 250000 requests
Completed 300000 requests
Completed 350000 requests
Completed 400000 requests
Completed 450000 requests
Completed 500000 requests
Finished 500000 requests

Server Software: vibe.d/0.7.21
Server Hostname: 127.0.0.1
Server Port: 8086

Document Path: /
Document Length: 13 bytes

Concurrency Level: 500
Time taken for tests: 16.471 seconds
Complete requests: 500000
Failed requests: 0
Keep-Alive requests: 500000
Total transferred: 81000000 bytes
HTML transferred: 6500000 bytes
Requests per second: 30355.65 [#/sec] (mean)
Time per request: 16.471 [ms] (mean)
Time per request: 0.033 [ms] (mean, across all concurrent requests)
Transfer rate: 4802.36 [Kbytes/sec] received

Connection Times (ms)

  min  mean[+/-sd] median   max

Connect: 0 0 0.2 0 7
Processing: 3 16 0.4 16 29
Waiting: 3 16 0.4 16 29
Total: 11 16 0.4 16 29

Percentage of the requests served within a certain time (ms)
50% 16
66% 16
75% 16
80% 16
90% 17
95% 17
98% 18
99% 18
100% 29 (longest request)