My estimations show a very good fractional shortening over 40% (EDD - ESD / EDD = 8.0 - 4.8 / 8.0). The healthy FS usualy pass beyound 35%.That means that maybe your myocardium works very well. Certeinly some mechano-dynamic properties of your ventricle is more important, than simple millimeters. In fact everything depends on your heart-muscle finction. So, it is not bad
It is also important to look at your Ejection fraction, which usualy works normal above 50%. However it alone is not a marker, since cardios watch the intramyocardial velocities and fibre shortenings due to a M-mode echocardiography/doppler. But... Do the surgery, before the LV begin to get tired of the large volume.
Ivo