The maximum angle of speedbrake defelction is different between the 320 and 321.
The 320 is capable of twice the surface defelection of the 321 but you have to have the auto-pilot out to achieve this angle.
Read FCOM 1 Flight Controls for both aircraft and you will spot the difference.
To answer your question - a good pilot can make the Airbus 'Slow Down and Go down 'at the same time (something a Boeing will not do)
Well handled you should be able to achieve 7,000 ft/min with little gain in forward speed