I'm looking for some recommendations for FTP-only hosting. Requirements are as follows:

Disk Space: 5-10GB
Bandwidth: ~50GB/mo
FTP User accounts: Probably around 100

I must be able to add users to groups, and set directory permissions based on user/groups. Ability to set up chroot jails is also desirable.

Ideally I'd like this hosted in Hong Kong, but US-based hosting is also acceptable to me.

Price is not a concern (as long as it is within reason); I'm willing to pay more for reliable service.

Thanks in advance for your recommendations.

(It doesn't really have to be FTP-only, if it comes with web/email hosting as well that's fine, but my usage needs are FTP-only).