I might be too late if Cheesehead has already made a decision, but I have a relevant setup and thought I'd give my $0.02.
I went with the Fireboard 2 drive (up to 6 thermistor and/or RTD probes; no type-k thermocouples) and the pit viper fan (slightly cheaper version of the pit bull). I am very satisfied with this setup and wouldn't recommend upgrading to the pro or the pit bull unless you expect most of your cooking to be at 450ºF or hotter.
While the pit bull is only $20-30 more expensive than the pit viper, I have never found the pit viper to be insufficient. Remember, these grills are extremely efficient--they don't require the same kind of airflow you would need in a kettle (or even other kamado-style cookers, for that matter). 10 CFM has always been plenty for my needs (I believe the pit bull does up to 25 CFM). If you expect most of your cooks to be high-temp cooks, I suppose the extra oomph from the pit bull could be worth the peace of mind. That said, as others mentioned above with the pit bull, I close the damper on my pit viper to avoid too much unintended airflow. I typically close it down to ~40%. I also prefer the plastic housing on the viper to the metal housing on the pit bull--I can pull my fan off right after the cook without burning my hand. To be fair, I don't know if this is an issue for the pit bull or not.
With respect to the probe types, I will admit that I rarely use more than three probes anyway--the three-port pro isn't likely to hamper you too much there. Even if you have, say, five butts smoking at once, you don't need to probe all five constantly--maybe one per grate level. The only time I will use more than three probes is when I want to keep ambient temperatures for multiple parts of the grill. For example, I might do a brisket with a point probe, a flat probe, one ambient on the main grate's right side (over the fire using grate splitter), and one ambient probe on the main grate's left side. Honestly, this arguably gives me too much data and I end up spending more effort than necessary trying to perfect my cook. Having said all of this, I have never been in a situation where I wanted to monitor a temp beyond the max temp for the probe ratings. If you're cooking at those temperatures (over 700ºF for the RTD probes), you might want to consider a different type of grill. Also, the hottest temp I cook at is for making pizza, and you don't really need more than the dome probe for that. As such, I wouldn't spend the extra $50 to get the pro, even if you never expect to use more than three probes.