Assume there would be 50 connections through the gateway, connecting to 11 resources.
My current Gateway is in our DMZ on a Hyper-V box. Both the host and the VM are Server 2012 (NOT R2).
VM has 8 virtual processors (Xeon E5-2660 @ 2.2ghz)
1 virtual network card
8gb RAM
There are 3 other VMs on the host.
I get intermittent reports of slow connections or slow RDP performance, but the main actual RDSH box isn't the bottleneck. That's got 32 core E5-2690, 32gb RAM, running 2008 R2 and has Enterprise SSD's. Obviously Internet connection plays some part, but at home I have a 30mbit connection and sometimes see a slow connection time, which makes me question the gateway.