Different front and rear wheels for d2r2 - any reason not to?

[moose8]

I'm doing d2r2 this weekend (the 100k) with my girlfriend - I want to make it as enjoyable for both her and me, and I was thinking I could take a bit of weight off her bike and mine by putting on some other front wheels I have. Other than looking a little silly, is there any reason I shouldn't do so? I've done d2r2 before, and ridden the course outside of the event, so I'm going in with eyes wide open as to whether or not it's a dumb idea for us to do together. For her bike I can match tire widths/rim widths, but for mine the rear wheel will be a bit wider rimmed than the front if I go with the switched-up set-up. My bike is a beast of a touring bike, but it's geared well for the hills, and the wheels are heavy so taking off weight seems appealing, while hers is an REI aluminum bike with some fairly heavy wheels. I bought a really light bike I was going to use, but then it was defective and the new frame is in transit, so I'm back to the touring bike.

Thanks for any advice.