I can't remember when and why the jumper was used on some rom chips. There is a thread about it here somewhere that spells it out. IIRC, some roms shipped with the wire installed and the instructions detailed reasons (MB revisions, some models, etc) to cut it. Yours was probably cut by the previous owner as instructed. Powering up should not hurt anything either way.
One of my A2000s is configured similar to yours. Mine has SupraTurbo 28Mhz, an A2091 with 2 Megs of fast, 1 Meg of chip and OS 2.1. It's one of my favorites, it still "feels" unmodified but is much faster than stock.
Something between the Supraturbo and the A2091 makes it take a liitle over a minute to boot. I've tried all the jumpers on both boards to fix this, no success. Other than this minor inconvenience, it's a very fun machine. It is surprisingly fast.
You got a great deal! I hope you enjoy it as much as I do.
