As a compiler, 3.65 is generally to be preferred over 3.0. Not only is it a newer iteration of ICC (and has more recent fixes), it supports more recent language features like (like 64-bit integers, as noted).
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That said, one big point in 3.0's favour is its INF formatted compiler documentation. 3.65 uses the NetQuestion HTML documentation system, which is bloated, intrusive, and in general a pain to use.
The NetQ service can be a PITA to setup, but once running I have found it to be incredibly valuable in terms of being able to scan through vast amounts of info that a newbie (like myself) simply has not "gut feel" for knowing precisely WHERE to find that info, thus INF files are great fountains of knowledge but it's a freaking steep mountain to climb when you are way wwwaaaayyyy down there at the bottom! lol
Robert, take a look at a couple of troubleshooting notes I saved up from 'way back when', they will help in getting NetQ up and running.
Re: the compiler itself: I have 3.6.5. here, as well as 4.x, both of which have multiple fixes (3.6.5 has two fixpaks, 4.x has a single one), but both have some one-off binary fixes that you used to be able to find here and there. Let me know if you want to see these and I'll toss them on my FTP server (PM me).