h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hello people.

I was just wondering if anyone knows how I could find out what grade I am on guitar. I am mostly self taught (for the past 6 years). I only started having lessons about 4 months ago and my playing has improved hugely and I have managed to get myself out of a playing rut (hurrah! finally!)
As I might have posted before, a while back my guitar teacher gave me a grade 5 piece, which, pretty roughly speaking I could play, except for some incredibly big stretches in a few bars which my hands just simply could not reach and I got frustrated with it.

As I understand from my former piano teacher, who estimated I was also about grade 5 on piano, grades aren't determined by general difficulty (or what you might consider difficult) its a combination of the scales, timing, fluency and all kinds of stuff. Anyone know how I could find out in a way that doesn't involve me sitting an exam?! I have never done a grade in my life, but I'm just curious to see where I'm at more than anything. I have got into altered tunings big time. It has totally changed the way I play so I have been able to attempt pieces I would have thought "too difficult" in the past. Do altered tunings have an impact on grades?
Thanks for your help

Kaz