Don't neglect evaporative / radiative losses!
At boiling they exceed (slightly) 1kW/ft2... the area being the opening of your kettle exposed to the air. I lose 1500 Watts to the air at boiling in my 15gal system which I've also verified experimentally by doing time-to-boil measurements and...
With regards to overshoot... I actually play a trick in my system because I'm crazy.. Use a 2nd heat exchanger on the recirculating circuit so that you can drop the temp if needed w/ a proportional control valve (which is also servo'd by the temp controller)
I built that in more to serve as...
Agreed.
A 2nd option (provided you really need the 120v in one connector), would be to make a bastard child adapter box where you'd have your mating connector spliced out to two separate plugs: #1) the 6-50 for both both ends of the 240 and ground, #2) a standard 120v plug where you just snag...
I'd argue that RIMs does not necessarily 'require' an extra heater element. If you size the RIMS heater accordingly, and have the appropriate plumbing to support it, you can use the RIMS heater as replacement for the HLT - serving as a tankless water heater. But given that the OP is limited in...