I've got quite the problem and I've been digging into it for a while.
I am on a MacBook Pro Retina, 2.7 GHz i7, 16 GB Ram, running Mavericks (10.9.1).
This is a work computer that was brand new in October.
It doesn't matter what browser I use, I've replicated it in all of them, but I am mainly using Chrome.
Some webpages will take up to 10-60+ seconds to load. It might take it 15s to load initially and then I can see in the bottom left corner as everything else is downloaded (very slowly) for the page to run (such as JavaScript and the images, anything that requires an extra request). I have really only noticed it since Mavericks but I wasn't paying enough attention before. I was on a WiFi only connection but I am now hard-wired and still have the same problem of pages loading slow.
I've done some digging in chrome://net-internals/#waterfall to see the events and in hopes that this is a low enough level to see what's happening. Here's the request info that seems to be where it's hanging:
t=11527 [st= 3] -HTTP_TRANSACTION_SEND_REQUEST
t=11527 [st= 3] +HTTP_TRANSACTION_READ_HEADERS [dt=3091]
t=11527 [st= 3] HTTP_STREAM_PARSER_READ_HEADERS [dt=3091]
t=14618 [st=3094] HTTP_TRANSACTION_READ_RESPONSE_HEADERS
--> HTTP/1.1 200 OK
Server: cloudflare-nginx
Date: Thu, 06 Feb 2014 20:44:23 GMT
Content-Type: text/css
Transfer-Encoding: chunked
Connection: keep-alive
Last-Modified: Thu, 08 Nov 2012 11:09:49 GMT
Cache-Control: public, max-age=2592000
X-Cacheable: YES
X-Varnish: 1986924772 1986903606
Via: 1.1 varnish
age: 0
X-Cache: HIT
X-Cache-Hits: 5
CF-Cache-Status: HIT
Vary: Accept-Encoding
Expires: Sat, 08 Mar 2014 20:44:23 GMT
CF-RAY: f8aad98b6f109be-ORD
Content-Encoding: gzip
t=14618 [st=3094] -HTTP_TRANSACTION_READ_HEADERS
This is a pretty quick example as you can see it's only 3 seconds. But this is on one request and most of the time that number is usually over 10 seconds.
Any ideas? I've done a repair of Mavericks but it's still having the problem. After a reboot the problem doesn't seem to be as bad but it's hard to say 100%. I've talked with the IT support at my work about it (it's my work computer anyway) and they have even less ideas.