What is the best way to get 7V from a benchtop 10V supply?
Best is hard to determine.. but here is one way for your 140mA (7V/50\$\Omega\$) load current: 

You can use an old-school LM317 regulator. 



In your case you can use 249 1% for R1 and 453 1% for R2 which should get  you close to
7V  out. The chip's power dissipation will be 0.15 * 3V + 0.005 * 10V = 0.5W, so a TO-220 case regulator should be okay in most circumstances without a heatsink. 

The somewhat newer LM1117 could be used but you have to pay a bit more attention the the output capacitance ESR to ensure stability (and the resistor values will be different because the reference voltage is 1.25V nominal vs. 2.5V nominal for the LM317). It does give you lower dropout voltage (it's a semi-LDO regulator), but since you have 3V to play with that's not required.