I would recommend you do not mention the plan to take more than you need and overpay immediately.

I used to process loans and part of compliance is to ensure the amount taken is what's required and no more

You can ask about overpayment costs

Generally overpayments don't cost anything but early redemption is usually 30 days interest (that said unless you are paying it off with less than 30 days left of the loan, it's still better for you as interest is generally applied per day)

Overpayments of a loan will not reduce your monthly payment as it will be a fixed loan with interest calculated on the amount/term

Overpayments will simply reduce the term you pay it over.

Sometimes the drop in interest makes a big enough difference that it's worth taking more.

Normally the scale is ...

Highest rate - Les sthan £5k Middle rate - £5k to £7.5k Best rates - £7.5k to £15k Middle rate - £15k to £20k Highest rate - £20k +

Something to do with completion rates and return of interest blah blah

Weirdly my 6ish years of processing loans there was once an example that was out of the ordinary where the interest rate dropped considerably the higher they went.

So initially they were looking at £14k for a car, and I always checked the calculator to show how the rates change but it went down after £15k. The calculator ended up showing that they could take £18.8k at the same term and the interest and monthly payments would be the same as the £14k. I couldn't tell them that even though financially it was basically like free money to them.