hi, I have a stihl fs 86 and have been asked to cut down a pampas grass plant it is over 8ft tall and around 6to7 ft around at the base, I have a grass cut blade model no.230-8 or a brush knife model 250 which do you think would be the best to use? im leaning towards the 230-8 as its a tough old plant but your thoughts would be most appreciated, thanks .