Speaker upgrades

Hi, im running a kef 5.1 2005.3 k2 setup.       Im happy with the system but wondered if i changed the Front centre speaker to a kef 3005 centre will i see a good improvement and is the speaker size in H/W/D the same as the 2005?

If i happened to be more adventurous as i enjoy my music as much as movies would be to use the monitor audio bronze BX2s for L&R front, 3005 centre and use the 2 spare kef 2005s from front L&R for a 7.1 configuration.    Would The monitors drown out the 2005 centre if i left that?    Help is very appreciated.  Thankyou daz