Yes, 5.0.01.0600 client should work with the ASA5510. I would recommend that you test the ASA5510 and VPN Client in the lab with all the features that you were using on the VPN3000 before deploying it in production. That way, if something is not working its easy to troubleshoot then trying to troubleshoot in a live network.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...