Samarchon,
If you have done install & upgrade in XE, you should not have any problem with ERP8.0 since the documentation stays the same with added features notes. I've done several installs and upgrades in the past 2 months and I can tell you that it went pretty good. Be sure to have the latest Planner ESU and SP on both Source and Target Release when you're doing an upgrade.
Hope it helps.
JL.