The difference between a 240 and 300 prode is only a few ozs. in weight and a couple extra shaft pieces in bulk. I've always had a 300cm and you're not gonna notice a difference in weight/size that's equivalent to a couple clif bars. Seems strange to risk having a probe that's too short for the rescue vs. having a longer one that might be just a few bucks more. It's not like you're gonna buy multiple probes, so why not get one that will work no matter where you move/travel?
The shovel you listed seems like a good option. I've always opted for one with a telescoping handle too. I used to have a T-handle, but now that I'm venturing over into mitten territory (instead of gloves) I replaced it with a D-handle.
Having a probe that would work everywhere does seem more practical to me.