In an OD loan, any amount paid over and above the EMI due is adjusted towards the "outstanding balance" but remains available for withdrawal. This reduces the interest due and there reduces your monthly EMI. So all the extra money from you future EMIs also shows up as a withdrawable amount .
In case of linked savings account like BoB, the outstanding balance is always adjusted against the EMI , if the linked savings account has some balance, then the interest due reduces, so the EMI offsets the principal itself. This reduces the tenure of the loan since your principal is being paid at a faster rate.
So in short, in SBI , paying extra money lowers your EMI, while in BoB it reduces your loan tenure
Hope this clarifies!
P.S. - BoB is more competitive, if you are looking for a loan in NCR then I can refer you to the executive who sanctioned my loan