there are many differences between those models that make the Reference 3 a better performer.
Frequency response:
Reference 3 - 43Hz – 35kHz
R11 - 46 Hz - 28 kHz
Output:
Reference 3 - 113.5dB
R11 - 113dB
Harmonic distortion:
Reference 3 - <0.5% 40Hz – 100kHz / <0.2% 200Hz – 2kHz / <0.1% 2kHz - 20kHz
R11 - <1% 33 Hz and above / <0.5% 80 Hz - 20 kHz
Construction:
Reference 3 - Better materials / wood finishes, more bracing, one piece front baffle, heavier, hand matched drivers, performance results included with speakers
R11 - Lower grade materials / vinyl finishes, less bracing, no front baffle, lighter cabinets, mass produced, no testing
The Reference are hand made and KEF matches the drivers to within 0.5db. They are more than a significant step up from the R11.