Here are first results of my very simple tests:
1. Take ordnance of 1xSC-500
With this bomb maximum ground level speed is about 460 km/h. After you release the bomb you would expect to rapidly increase your speed, but it remains still 460 km/h and looks like you would have the weight of the bomb still strapped on. Well you may think that it is the cause of the hardpoint, but no as we come to the second
2. Take 1xSC 500 and 4x50 ordnance
with it you get your maximum speed of about 430-440 km/h at ground, after you drop it all, what happens, nothing...your speed remains about the same.
3. Take 2xaditional droptanks
with them your ground speed is about 490 km/h, after droping those it remains just about the same.
Conclussion: After droping your ordnance you would expect a great performance increase (degraded a bit by hardpoint), but it looks like the weight remains on after droping it. I don't know if it applies also to other planes, but these are my findings regarding the A5