Each speedo is different, and you can't say that taking the red lead out applies across the board. LRP and Tekin work with the red lead in but you must not switch the speedo on at the switch with either - only the receiver pack. The capacitor will make no difference at all with a 1S pack on your Mardave. I've run an RS with a LiPo receiver pack and not had any problems, but that was using Futaba 603FS receiver and 9650 servo - high-quality parts. Your mileage may vary...
Tekin do not recommend using a LiPo receiver pack straight into the receiver. They accept a LiFe as it is lower voltage. If yours is a Tekin RS, RS Pro it takes 3-cell inputs. If it is, then the correct way to wire it is as per the attached.
This wiring method will allow you to use the voltage regulator in the speedo. As it is a 6v regulator, it means you no longer have to worry about your receiver being over-voltage, or the servo. It also means that you should be glitch-free when using good quality receiver and servo. Wire it up like this and then switch it on from the speedo switch. HTH
PS - yes, you should use about 80-100mAh per race, so a 350mAh pack is fine. I could get two eight-minute races out of a 250mAh pack. Don't forget to recharge it otherwise...
