Nifty PSU Bank was the top-performing index on NSE in an otherwise dull session on Monday, with 11 of the index constituents at fresh 52-week highs. Over the longer term, independent market expert Sandip Sabharwal does not recommend to keep on buying PSU banks as from this quarter or next quarter onwards, we will start seeing some uptick in NPAs and a squeeze in margins which was not there for the last two quarters.