I been into Mustangs for a long time, and trucks for a year or two; Here is what I have come up with from spirited driving.

The t5's case will flex and you will lose 3rd gear and the cluster quickly.

The M5OD will spit the input shaft and wear on syncros

The NP435 with take all you can throw it at... But with granny gear and slow shifts.

I haven't used a ZF, but I have heard they can handle it... With granny gear and slow shifts.

I'm in the process of building a shortbed 2wd truck right now with a 429 and 4 speed toploader. I'm hoping the toploader holds up, and from what I have read, it should.