I fly a Bulldog based at Prestwick, and have been to Sywell twice, and Breighton a number of times. Weather does play a big factor in the routes - both times heading down to Sywell we had to fly from Carlisle over to the East coast before heading South, but did once manage to come up via the Manchester low level corridor (popping into Barton for some fuel) and routed up the West coast.
The key is to plan both routes - we found that even with lowish cloud you could get from Carlisle over to the East coast by heading along the Derwent -> Hexham -> Haltwhistle route.
I'd agree with Dan about stopping at Breighton. Great wee airfield with cheap self service fuel and some interesting aircraft to see if you have the time.
Feel free to pop into Prestwick and see us!