The 400E is 10% heavier as the 300E...these 10% are to be found in the front of the vehicle...
If I had a set of 300E lowering springs lying on a shelf and a 400E standing besides that shelf...I would give the springs a try to determine for myself whether they would be stiff enough or not.
When you have to buy these 300 springs first to have them installed by a shop (when you don't have the facilities yourself), I would consider buying myself some 400 lowering springs.
If you cannot change the springs yourself and the 300 springs end up being too soft, lowering your car will become rather expensive.
with a minor 600+k