Potential gravity from Orange and Grape Juice Concentrate

I have a test batch of mead going now, its been in primary for 5 days now
1lb honey
1 12oz can grape juice concentrate
1/2gal water
premier cuvee yeast

#1 This is a low flocculation yeast and I just took a reading and its almost 10% abv!
OG 1.098 Gravity after 5days 1.025
I know that one packet of yeast is obviously over pitching but I wanted it dry
Did it ferment this fast because it is over pitched.

#2 I dont know how to predict the potential alcohol when I do a full size batch of this because I dont know what the fermentable sugar is in grape juice concentrate. obviously I can figure the potential alcohol production based on just the honey...anyone have experience with this???

anyone? thoughts? kahuna, malkore, your input would help im sure

honestly what I'd do is make a pitcher of that juice, probably 2 quarts, so a half gallon. take a hydro reading in the pitcher, divide by 2, and that's the gravity points it will all at 1 can per gallon.

thanks yeah I thought about that but not until after I had to poor a little out to add the rehydrated yeast back in

so I did some number crunching and got the gravity for concentrated OJ and Grape juice in one gallon.

OJ gives 1.032 in one gallon h2o
Grape Juice(welches) gives 1.017 in one gallon h2o