Overpaying and shortening the mortgage term

Hi everybody,

It's been a while since I was last on these boards, however, I'm in the process of potentially changing mortgages and would like some advise on the above.

I'll be switching from a fixed rate to a tracker (see below for details), and was wondering if it's worth shortening the term to 19 years, as well as continuing to overpay? Are there any significant advantages/disadvantages to doing both? Or would simply overpaying by itself be enough?

Current deal:
Outstanding mortgage £90k
Interest rate: 4.79%; 5 year fixed rate until 30/09/2014
Term: 21 years 11 months to go
Standard payment: £580.00 per month
Current payment: £695.00 per month (which is the maximum 20% overpayment allowed)
ERC: £1450

Proposed deal:
Interest rate: 2.79%; Lifetime tracker at 2.29% plus BBR
Term: 21 years 11 months
Fees: Fee free :)
Standard payment: £457.00 per month
Proposed payment: £695.00 per month

Proposed deal (but with term amended to 19 years):
Standard payment: £510.00 per month
Proposed payment: £695.00 per month

It appears that all it would do is make the standard payment go up (obviously due to the shortened term), making it a little less flexible. Although it would still be £70 less than my current mortgage.

Thanks in advance for your input.