Hi. Welcome to the digideep forums!
Whether you think upgrading to the A640 pretty much depends on your view of the differential features. As far as I can see, there’s not much difference between the A620 and the A640 apart from that the A640 is a 10Mpx camera whilst the A620 is a 7Mpx camera.
The A640 works from 4 AA batteries, so if the A620 works from 2, there might be better endurance from the A640. I’m not sure how big the screen on the A620 is: the A640 has a 2.5” screen, so if that is bigger than the A620, then you might consider that a benefit worth having also.
I have read some views that the 10Mpx on the A640 is a ‘bridge too far’ i.e. that Canon have tried to cram a few too many pixels onto the same sized sensor, and actually sacrificed quality compared to the 8Mpx A630. Whilst there is the possibility that this is the case, I personally have not seen comparatives that either support or debunk this view. I have seen underwater results from the A640, and I have to say I’ve been impressed. I haven’t seen anything shot on the A620, so again, no comparitive unfortunately!
Personally, I think I would probably get another A620 and avoid the additional cost of a more expensive camera, and a new housing. Your mileage, however, may vary!
good luck!
