4 dedicated lines to 4 machines will NOT work unless they are on different subnets. This would require 2 Network cards per client machine. One NIC would be on the normal subnet, and another NIC would be a different subnet, going straight back to the server. Each of the 4 NICs on the server would need to be on a different subnet and each one dedicated to a client. This is a dumb design and will not gain you anything beyond connecting 1 server NIC and the 4 clients to a decent switch. It will however increase your overhead support, as in, you will have a bigger headache. If you need faster speed, go 10Gbps.
If you make an attempt at subnetting out the different NICs on the server to a switch (with VLANs), you then have a problem with your bottleneck being the gateway for those devices.
If you just randomly assign a different subnet on each NIC (without VLANs) and plug them into your switch, you are just breaking your network.