Moving the mortgage to a new property will mean pushing the interest up an extra 1% to 2.5 whilst still being a tracker...
My salary is benchmarked and I am 5 years off the top of my scale which is approx 85k ... this added to the 25k my partner is on will bring the total earned to 110k per annum in 5 years time.
Does any of this count for anything?
How realistic is your 310k valuation?
How old are ye, boi give mortgages up to 70, some others 68, it's likely longer helps your chances. To maximise exception potential it helps to take as long a fixed rate as possible, but rates are more like 3.3 for 10 Yr fixed. That said, it's unlikely they'll offer you what's needed to fund the 490k purchase, they'll offer 4 times possibly, but anything above that may need higher salary levels etc.
As others have alluded to, you should look at the affordability of a prospective mortgage of 400k, it woukd be a pretty large step up on current savings levels and current mortgage repayments by the looks of it.