Thanks for your insight Peregrine. Apparently you and I ran into the same search engine difficulty as I started my own thread in much the same vein.
For me the big thing with the TX-42 is to make up your mind about what role you need it to fill at the start.
If you want them to kill AV 12 +, go with the Twin-linked Fusion Blasters and be aggressive.
If you want them to kill MEQs and TEQs, Twin-linked Plasma Rifles and be aggressive.
If you want to kill infantry and AV 10 to 12, Twin Linked Missile Pods, a Disruption Pod and stand back.
If you only want to kill MEQs, go with Rail Rifles, a disruption pod and curse yourself for not using Plasma :-)
If you want them to be movement blockers, save the points and use regular Piranhas.
So look at your army list and see what element you are lacking and build your Piranha choice around that.
Also, that turn 1 Full out is very handy. It gives you the ability to be 48 inches from a target on turn 1, but in rapid fire range on turn 2, plus you get a cover save during the enemy's intervening turn. So don't be afraid of the short range, just ram it down their throats and acknowledge you may be down a skimmer at the end of turn 2 or 3, so make it count.
On the other hand, the Missile Pod variant, with the 12 inch move, can start raining fire down on a target 48 inches away on Turn 1 and keep itself away from a lot of hazards and use the Disruption Pod and LOS to cover you from most of the rest.
Me, I like to preserve my forces so the Missile Pod variant is going to be my preferred option, but the Plasma variant may end up being my solution to the hordes of undead robots that I am currently plagued with.