opinions on xen

xen probably won't be any faster than KVM was for you. You have at least one thing working against you. The biggest issue is RAM. 1GB is not a whole lot to run your host OS in and then still try to run a guest OS in. Even swap won't help you much here, because swap is soooo much slower than physical RAM. Second, you may not have same architecture paravirtualization support in your processor (intel vme). IF you do, make sure it's not disabled in your BIOS, as this is often the case, especially in older systems. If you want to check if you have the feature available, either check /proc/cpuinfo or look up your processor's model number on-line.

good luck.