LF - you don't say what kind of aircraft it is (I'll have to assume sort sort of corporate jet/business airliner) - but have a look in the flight manual and calculate the runway length reuired for departure at MAUW.
Just to be on the safe side, use an uphill slope, 25 degree OAT, a 10 knot tailwind and at least double the density altitude.
Then have another look at the runway length available at Weston - I'm sure you've already done this once if you've already planned the trip before - and then you can make the decision as to which airport you NEED for a departure at near MAUW.
Are you doing this trip IFR? Or is that phrase "NEED" to leave Dublin at 7:30am more of a "we are going to be in trouble if the weather is crap at 7:30am"?