I think I may be getting slightly confused with the MTU values. I've set them subsequently to posting the config, which is why they aren't showing up. I found a few posts on Google where people had done similar to me, and stated that you had to match the MTU to the packet size you settle on doing ping -l -f. It doesn't seem to have made any difference.
For clarity should I just set MTU 1492 on Dialer 1 and MSS 1452 on Dialer 1 too? Do I need to set the MSS on any of the VLAN interfaces?
Oh I tested the VPN from home last night it works fine. I realise now that testing it from the web server doesn't work (1723 isn't opened) and nmap and shields up were correctly reporting that the port is open.
Edit: additionally I find that if I disable the Cisco FW downloads work fine. We can surf the net with the FW up, but no downloads or speed test
Not sure what in the FW might be blocking it, but imagine maybe it isn't necessarily specific to using PPPoE like this scenario...