Relative novice only done two Biscay crossings(going south)One was in mid September and we had perfect sail,wind on the beam or just aft,trimmed the sails twice a day whether they needed it or not,and read Reeds cover to cover 6 times.
The only thing that worries me is the "planned" bit,good weather window is pretty essential,and despite what the overall statistics might say these can happen at anytime through the year!
The later you leave it the shorter the weather windows as the lows track in faster, ith the lack of big highs to slow them or send them north.
The trouble with Biscay is that for most yachts less than 40' it can take more than three days and three days is as long as you get an accurate forecast for, so you can find your self getting the front end of a low as you arrive off the Spanish coast.
I've had a complete kicking in Biscay in November, for that reason, we'd waited in Falmouth for two weeks for a window, but it wasn't quite long enough. The boat was fine but the crew were green.
But after two days you have plenty of sea room, so its not as scary as being off the Brittany coast in a blow.