Pix question

5 PIX 501 are connected back to a PIX 506 (S2S VPN). each site has a 6 MB DSL dynamic IP (4.9Mb tested and meseured) the 506 has connected to a 3Mb static IP line . they have to come to 506 in order to go to Internet, dont ask why :) even with single user, the speed wont be better for 600KB for the user behind the 501. I am guessing one reason is the VPN and encryptions. Security is not a concern for this project, and they only need a connectivity to main site to go to Internet. If I had those site as static I could just open them on 506 but with dynamic IPs I think the only way would be VPN??? am I right?

Also I am using DES, is there any other method with less ovehead? not sure how to speed up the connection?

Thanks in advance for any help. Rob