asa 5520 vpn client perfomance

Hi All

I'm currently working on a new client vpn solution for giving remote acces using the cisco vpn client. But regardless of encrytion methods, inspection level etc., I'm not able to get the throughput above

10Mbi/s, which is far from the 200+ Mbit/s the ASA 5520 should be capable of. Some good ideas or link to literature about vpn performance?

Thanks

/Soren Hansen