Six of the top-10 most valued firms together added Rs 86,847.88 crore in market valuation last week, with HDFC Bank and Reliance Industries emerging as the biggest gainers in line with an overall optimistic trend in equities. Last week, the BSE benchmark climbed 657.48 points or 0.84 per cent, and the Nifty rose 225.9 points or 0.95 per cent.