Temperature coefficient of nichrome wire is pretty low - not a problem for current changes here. The 6.5 amp theoretical would go to 7 amps - maybe.
Parallel a couple of rectifiers. Put a .2 or .5 ohm resistor in series with each to keep the current division reasonably equal. Watch the wattage on the resistors.
That (current coefficient) lines up with what I observed in my smaller project, granted that I was starting off at half voltage to begin with, so I never got close to the element being “bright”.
Noted on the resistors - good point.
Roger that. Any two diodes, even from the same manufacturing batch, will have somewhat different forward voltages for a given current. So while they will tend to share the current, it won't be 50/50.
Placing a very low resistance in series with each diode means there will be a small V=I*R voltage drop across the resistors, which added to the forward voltage of each diode, will tend to equalize the current in each parallel leg.
You can do that with two, three, or more diodes if needed.
I use as a rule of thumb to drop 0.2V across the resistor (assuming silicon diodes with 0.6 to 0.7 forward voltage). And definitely watch the wattage, it can be surprising at high currents.
YMMV.