I have a pix 515E in failover mode running ver 6.3(4). We want to upgrade to 7.x but do not know which version of 7 to start with. Can anyone tell me the best path to follow. Can I upgrade from 6.3(4) to 7.2 without first upgrading to 7.0.
Yes, you can but it is not recommendable. Please upgrade first to 7.0.7 which is the latest one within 7.0 train. Then you can go for 7.2.x
Please bear in mind that there are some commands that have been deprecated from 6.x to 7.x specially on VPN: