A report issued this week by Goldman Sachs analyst Andrew Lyons articulates some of the factors driving the recent outperformance of listed regional bank stocks compared to their larger rivals.In the last month the ASX financials index has risen 5.5 per cent, but Bendigo Bank and Bank of Queensland have each rallied by more than 10 per cent.Recent mortgage rate announcements from the regionals have contributed to their share price strength, with Lyons estimating the repricings could have a significant impact on forecast earnings.BoQ announced on 25 June that it was hiking variable rate mortgages for owner occupiers by 9 basis points while investors would incur increases of 15bps.Bendigo followed on 13 July, flagging increases of 10bps for owner occupiers and investors.Number crunching by Lyons indicated that each of the regionals stand to thicken their net interest margins by 5 basis points.The relatively high exposure of Bendigo and BoQ to mortgage lending means that such margin improvements could boost the earnings per share of both banks by more than 5 per cent.However, the earnings benefit to the major banks of similar home loan repricings would likely deliver more modest earnings benefits.The Goldman Sachs' number crunching suggests Westpac would be in line to derive the biggest earnings uplift within the cohort of big banks in the order of 3 per cent, with the other majors likely to each derive earnings boosts of around half the level the regionals.While the ACCC investigation into the mortgage market and the hearings of the Hayne royal commission are keeping a lid on repricing moves from the majors, they are forced to absorb the margin erosion.Lyons estimated that the rise in wholesale funding costs has wiped up to 3 bps from the net interest margins of the major lenders.