Anderow
I can remember training for an IR in a PA28 We were in an airway at FL80 in solid IMC when the instructor told me to hold my altitude.
I pointed out that I had max power and sped was back to 75 KTS and we were going down.
He quickly asked ATC for a lower level and we were cleared to no lower than FL60
we sailed down through FL60 and only stopped at 4000 feet with terrain at 2300 feet below
had the icing level been lower God knows ?
don't mess with icing in a non deice anti ice capable aircraft.
If you do carry extra speed to a normal approach and landing as your stall will be higher and although the ice may melt off in certain areas you may have quite a buildup on other areas of the airframe
Pace