I should mention that the statistics of d6 open ended dice were discussed in
another thread, and many results apply as well to d25oe throws.
In particular, for X=24n+r with 1<=r<=24, the probabilities of getting X from 1d25oe and 2d25oe are
P(1d25oe = X) = 25^(-n-1) and
P(2d25oe = X) = [ (26-r)24n+r-1 ]/25^(n+2)
From the latter one can do the summation to get P(2d25oe > X), which gives the probability of throwing larger than X, and then one more summation to get a table like on p.5. The actual numbers are likely to ugly, as already the result for d6 involves some funny numbers. Maple/Mathematica is strongly recommmended.
The method of the previous post possibly also works for central values, but underestimates the tails, as the distribution is exponential instead of normal (Gaussian).
Somewhat unrelated, I'd like to point out that for any open-ended dice 1dNoe, the average value differs from that of corresponding dice by exactly 1/2: XbarOE = N/2+1 (for normal dice (N+1)/2). For N=25 this gives XbarOE=13.5, and for two independent dice <2d25oe> = 27.