Is it worth an early exit?

£120,000 outstanding
£140,000 value
Natwest 5 year fix at 5.99% due to end Dec 2014

I've found a 90% LTV 5 year fixed product with no admin fee at 4.20%.

http://www.thehanley.co.uk/hanley_5_...ixed_5051.html

The svr it drops on to after the fix is terrible but I'd budget in a mortgage move and with overpayments unless my house decreased in value dramatically then I'd be ok for another product.

One capital overpayment per year though up to 10%. There isn't any issue with exceeding the 10% but I've never heard of overpayments being limited to one per year. The product doesn't say if its annual interest or not so what are the big cons with this?

I'm not currently in the uk so I can't check my paperwork to find out what the early repayment fee was on my current natwest product so if anyone knows the numbers on historic products please give input!

I need someone that's good with the compound interest numbers to let me know if an early exit fee would be worth it in this scenario. If nobody knows the natwest figure then I'll add it to the post next week when im back.

Thanks MSE regulars