If you have gone for the zLinux virtual server option as an alternative to multiple external servers then its my guess you will want to maximise the advantage by utilising the superfast speeds of the mainframe.
Putting in Hipersockets gives you high speed network connections between all your virtual Linux servers and LPARs running z/OS or S/390, that looks and feels just like TCP/IP. Of course it is not TCP/IP - the connections move data around from one memory location to another, there is no physical cabling involved. IBM quotes the following improvements in speeds "Benchmarks using two LPARs each with four CPUs, each running 31-bit Linux kernal 2.4.7 on a zSeries 900 HiperSockets demonstrated up to four to six times more throughput than a single Gigabit Ethernet for batch streaming traffic,and up to between two and five times more throughput for interactive traffic. This can translate into shorter batch windows and faster response times".
IBM documentation on Hipersockets
IBM performance evaluation
Hardware - Hipersockets