Hi,
I view RemoteFX as a LAN protocol still - you'll need to implement PCoIP or HDX (Citrix). As you already have Server 2012 and RDS, you're already using RDP - are the clients using RDP 8.0 (Requires Win 7 SP1 or Win 8 if I recall)?
My suggestion would be to look at PCoIP for Server 2012:
http://www.teradici.com/pcoip-solutions/rdsh-solution/overview.php
Alternatively you can deploy Citrix XenApp to try the HDX protocol on the RDS Server.
Both can deliver the experience you require but may require tweaking to function well over the link speeds and latencies you are experiencing. They both provide tools for analysing their use which greatly helps diagnosing the initial deployment. Google for best practices guides and they should point you to relevent tuning documents.
Regards,
Mike