I have a student loan question...

I am currently enrolled with auto debit for my student loans - in turn, Sallie Mae gives me a .25% interest rate deduction. If I stop auto debit - they will tack this .25% interest rate back on my loans.

My situation with the loans is somewhat unique as I live/work in Europe and every few months I transfer cash to my US account to cover the student loans for a few months. You cannot pay student loans with a foreign account. For example - In December I transferred $4,000 to cover what I've budgeted for my student loans January - April. $496 monthly payment + $504 additional/month. So when the transfer cleared my $496 January payment posted as scheduled, and I submitted $2,016 to cover the extra payments Jan-April. But I leave the remaining $1,488 in my account to cover the auto debit payments for Feb-April. Would I be better off if I just posted all $4,000 at once? The due dates for my loans also push back when I pay more than the monthly due.

My current rate for my loans is 6.55% and 6% - so if I end auto debit it will increase to 6.8% and 6.25%.

Here is my current loan load:

$15,954 @6% - next payment due: 3/3/14 ($83.86)

$10,903 @ 6% - next payment due: 3/3/14 ($57.31)

$2,261 @ 6.55% - next payment due: 5/3/15 ($69.89)

$7,848 @ 6.55% - next payment due 5/3/14 ($69.54)

$12,778 @ 6.55% - next payment due 4/3/14 ($111.47)

$11,763 @ 6.55% - next payment due 5/3/14 ($104.64)

Auto debit clears every month an pays the monthly payment (amount in parentheses) against each loan regardless if a payment is "due" or not.

I'm beginning to wonder if auto debit is actually holding me back... and this .25% rate reduction is doing more harm than good? Does anyone have a formula or a way to figure out if it makes sense to eat the .25% to give myself the ability to reduce the principle sooner? Obviously the interest will be higher - but the amount the interest is being calculated on will be lower...

I know this is sort of an odd question, but I can't figure out a way to calculate this myself. Let me know your thoughts.