Heating wire filament with low voltage high current?
Nichrome has a certain resistivity (which varies with temperature and exact alloy). To use a lower voltage means you have to have lower resistance, all other things being equal. Resistance of the wire is: 

\$\rho L/A\$ where \$\rho\$ is the resistivity of Nichrome, L is the length of the wire and A is the cross-sectional area of the wire (\$\pi r^2\$ if the wire is round). 

In your two examples, the resistance is 25m\$\Omega\$ or 10\$\Omega\$, a 1:400 ratio. 

If the wire is fixed length (for example for a wire foam cutter) then the lower voltage wire must be \$\sqrt{400}\$ times larger diameter or 20:1.  

The heat loss will be a bit different with the different sizes of wire. There is a good set of tables on Wikipedia.