'Out Of Memory' error in LoadUI

I believe AndyHughes has posted about this issue before, but I'd like to see if anyone can help.

I am trying to achieve 300 transactions/sec by running a test from an Amazon EC2 image. The details for this are:

Microsoft Windows Server 2003 R2 Datacenter x64 Edition
Intel(R) Xeon(R) CPU
7.50GB RAM

LoadUI version - 1.5.0

I have increased the amount of memory used by the JVM so that it resembles the following:

<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="file:." href="loadUI.jnlp">
    <information>
        <title>loadUI</title>
        <vendor>eviware</vendor>
        <homepage href="http://www.loadui.org/"/>
        <description>loadUI</description>
        <offline-allowed/>
    </information>
 <resources>
        <j2se version="1.6+" java-vm-args="-Xms128m-Xmx1024m -XX:MaxPermSize=128m -Dsun.java2d.noddraw=true"/>
        <extension name="JavaFX Runtime" href="http://dl.javafx.com/1.3/javafx-rt.jnlp"/>
        <jar href="lib/loadui-launcher-1.5.0.jar" main="true"/>
        <jar href="lib/org.apache.felix.main-3.0.9-patched.jar"/>
        <jar href="lib/commons-cli-1.2.jar"/>
        <jar href="lib/jna-3.2.7.jar"/>
        <jar href="lib/platform-3.2.7.jar"/>
    </resources>
 <security>
  <all-permissions/>
 </security>
    <application-desc main-class="com.eviware.loadui.launcher.LoadUILauncher" />
    <update check="timeout" policy="always" />
</jnlp>

I'm reluctant to use agents at the moment because I believe I can get much more out the tool than what I am currently getting. Can anyone help me with this? It is quite urgent

Cheers

Mike