Over the last five years the S&P/ASX 200 Index (ASX: XJO) is up 46.93%. A large influence on this index is the big four banks, which represent four of the largest seven companies on the ASX by market capitalisation. 

While all big four banks have risen over this span, two have more than doubled. 

Commonwealth Bank of Australia (ASX: CBA)

Commonwealth Bank has been the bell of the ball for ASX bank shares over the last five years. 

In June 2020, its share price was sitting around $67 a piece.Since then, it has experienced record high after record high, and its share price now sits at $181.40. 

This represents a 169.46% rise. 

That means a $10,000 investment made 5 years ago in CBA shares would now be worth $26,946. 

National Australia Bank Ltd (ASX: NAB)

The second best return over the last five years from a big four bank is from NAB. 

While it hasn't risen as much as CBA, investors who bought shares in NAB five years ago wouldn't be complaining. 

Its share price is up 110.17% over that period. 

A $10,000 investment in the big four bank's shares would today be worth $21,017. 

Is the party over for these bank shares?

Despite both bank shares outpacing the ASX considerably over the last five years, experts think it might be time to take profits.

Brokers seem to believe that Commonwealth Bank shares current price is overvalued. 

However this rhetoric has been consistent for some time. Meanwhile, the share price has continued to rise, making it difficult to anticipate how much room there is for further growth. 

Broker Bell Potter has a "sell" recommendation and $119.22 price target – which infers a 34.27% fall from its current price. 

Brokers also seem cautious about short term upside for NAB shares after such a strong run. 

Late last month, Macquarie placed a price target of $35.00, indicating more than a 10% downside from its current price of $39.07.

Bell Potter is even more pessimistic on NAB shares, with a price target of $33.50.