You will not see this problem when testing into a dummy load. One 4n7 or 10nF on each side of the amp will solve it. This will of course reduce the HF response of the amplifier to something much lower than 900kHz. If you need more power then go to class D or E with square waves. Class D amplifiers switch the FETs on and off.
Efficiency is high but depends on the devices output capacitance.
Class E amplifiers contain components to compensate for this capacitance and have even higher efficiency. Contrary to popular belief, switching type amplifiers can be used for linear amplification. It's not easy, but amplitude variations can be digitally modulated onto the supply Voltage, while variations in phase can be modulated onto the drive signal. Photo G4VBH G0MRF tuning for resonance on 136k as visiting A45ZN looks on. 250 Watt amp and driver with keyer and LF synthesizer on top.