Thanks for all of the feedback! There are some gems. Especially from Allan King- "test records cannot be deleted from forms". That's bizarre & a little frustrating, but good to know before-hand.
We're in the process of road-mapping the integration of multiple systems (E9s, E10s & Marketos) into a single E9 infrastructure. We're meeting with the Eloqua migration team to investigate EVERYTHING that will be impacted if we move the main E9 install to E10 before integrating the others. I'm an E9 admin, but operate in our E10 installs as well and would agree with Jennifer Gonzalez (Re: "My personal preference in E9 because I am a geek at heart and love program builder"). Glad to hear from the E10 veterans on your perspective! I want to be sure we know what to expect.