Very good question.
I believe that an increased clearway will lead to an increased MTOW but will also lead to a lower V1.
Lets start by the definition as always...
TODA = RWY LENGTH + FULL CLEARWAY
Therefore if clearway increases, the TODA will increase as well thus allowing a higher TOW.
However, assuming that the RWY length is unchanged, a lower V1 improves the stopping distance on the RWY.
It should be appreciated that using 50 meters of clearway and lowering V1 just 1 knot is enough to raise the TOW by almost 500 kg (source taken from the book "Aerodynamics for Airline Pilots"; exemple from a DC-9).
In conclusion, if you have a long stopway, V1 can be increased but in the other hand, if you have a long clearway, V1 can be reduced.
For your other question, I don't know...
I have to go back in my library and dig into the books.
Will let you know if I find something.
Cheers.