I can't really burn any of the gear in beforehand
Why not? I would strongly suggest you burn in your equipment at home for at least 25-50 hrs. before using it to decide on anything. I would never evaluate speakers with brand new electronics, especially tubes. IME tubes can vary wildly in sound within the first 25 hrs. and may not settle in until around 50 hrs.
If it is because you do not yet have any speakers I would go to Goodwill or Craigslist and buy an el-cheap-cheapo pair to load your equipment for burn in of your new gear.
I might be better off with a smaller cheaper speaker that my amp will find easy to drive vs a more expensive, potentially nicer sounding speaker that my amp would find more difficult (not straining, just more difficult) to drive
Do not equate size of speaker to dictate which speaker might be able to be driven easier or be more difficult. Not a good indicator.