Oh - and put me down 2nd in line behind big green if you buy an ST-5 and then decide to sell it.  I'm planning on buying one - sometime in the next 6 months?

We'd really need a little more information to help with this.  What kind of pump is it?  Submersible pump or topside centrifugal?  1 or 3 phase?  If it's a 1 phase submersible, is it two wire or three wire?  The starting needs vary quite a bit depending on what type pump you're using.  Submersible pumps are one of the most difficult loads to start, they typically have a full column of water from the pump to the surface to start against.  The two-wire single phase pumps are typically even worse.

Then there's the question of what kind of generator - a Lister type setup with huge flywheels and a well-built permanent magnet alternator will start a much bigger load than a big-box-store high RPM engine with a poorly regulated generator head, even if both are rated with the same HP engine.

Unfortunately, there's no magic formula that will really tell you if it will work.  Various people have widely different "rules of thumb".  Whatever you get, try it before the power goes out and it's crunch time!

And should I be concerned about that yellow cap, looks like from a can of PB Blaster?  I'm guessing it WAS stuck.