I'm not a fan of mashing at high temperature to enhance sweetness. After almost 15 years of beer judging, I have found that one of the cardinal sins of many homebrewers is creating beers that fail to finish dry enough.
If sweetness is desired, reduce the bittering and allow the sweetness to exhibit that way. In my opinion, raising the mashing temperature is best reserved for those cases where the gravity of the wort is low and the brewer is trying to improve the body via reduced fermentability. In a beer that has adequate gravity in the first place, reduced fermentability is not the way to achieve a sweeter or maltier perception in the beer...reduced bittering is.