If you’re experiencing really slow downloads from the iTunes store on TELUS Optik, it could be a problem with your DNS servers.  I think by default the DHCP server on the Optik router configures the clients to use the router as their DNS server.  The router is configured to use the servers:

• 75.153.176.1  (ns1.dns.telus.com)
• 75.153.176.9 (ns2.dns.telus.com)

I think that either the Optik router or the TELUS DNS servers are a bottleneck here.  I guess  that for some reason, iTunes needs to do a lot of DNS lookups when it transfers data?

Anyways I changed my clients to use the following DNS servers:

• 8.8.8.8
• 8.8.4.4
• 208.67.222.222
• 208.67.220.220

The first two are provided by Google, the last two are provided by OpenDNS.  iTunes download speed went from ~200KB/sec to ~1.5MB/sec.  On Mac OS X, change the setting in System Preferences → Network → (Select your Network Connection) → Advanced → DNS.