Zuluwoffle,
I have a 650bcvrr and am happy with it.
the 600 is a smaller spool diametre than the 650. I think it means 6 inch against 6.5 inch. Therefore the 650 should hold more line, and also allow the line to peel of faster giving a longer cast distance for the same effort. The rapid retrieve is good off the rocks with lures...but the whoel thing gets heavy.
As for the surf rod, i don't know much about the rods you mention. I always thought that the Alvey rods seem to have a small stripper (first guide stainless steel). Some say that this would impeed your cast distance, but I am not sure.
I use a Gary Howard "Castaway" surf rod and am happy with it. It has paid itself off in Fish fillets over the last 5 years.
My mate has a 700 series Alvey, and he is able to cast further than me , but he is also taller, and has a different rod, and about 20 years more practice at casting.
Some guys will also say to upgrade the drag washers, but I have not done so.