I got an excellent plot off my GPS from my recent real turnback with a partial loss of power. It helped a lot in my personal debrief.
Backpacker - I do a lot of assessment of flight test plans and flight test reports, but within a structured test environment. I would recommend if you are going to do this safely that you make sure you understand briefing and debriefing for flight test, get somebody else to listen to and critique your brief, understand the use of test cards, and probably fly with an experienced pilot as a safety observer. Also make sure that all of the aspects of flying you'll be demonstrating you are fully current in, before putting them together. The standard technique for assessing difficulty of flying a manoeuvre (usually referred to as "pilot compensation") is the "Cooper Harper Rating Scale" - there's a lot about it on the web, but you may find it useful to run your CH task construction past a test pilot who has done the formal training in its use.
G