I created a VPN connection on my 2008 server to my home office router and it barely uploads a file at 150kb/sec I can ftp at 5mb/sec to the same network from the same server.
It sounds like you have some weak under powered links in your network.
VPN is processor intensive. The more powerful the processor in your router(s) when combined with lots of RAM should result in improved through put.
With powerful off the shelf equipment you should not lose more than 15% - 25% of your upload and download speed. With equipment designed to handle VPN processing the loss could be as little as 5%.
Or look at installing DD-WRT X86 or RouterOS on a PC with a high powered processor and lots of RAM.
While for some people PPTP runs faster the security if offers is so minimal that it isn't really worth the overhead it takes.
