Iv never been a big fan of bump keys its always been too awkward to hold the right tension on the key while bumping it.
messing around with a dimple lock the other day i decided to try bumping with a tension wrench.
i machined a slice off the side of the bumpkey just enough to get a tension wrench in.
clamped it all up in the vice and used a weak spring as a damper.
bumped it open with no problems at all and found it much easier to maintain ultra light tension.
Just thought id share that as im sure im not the only heavy handed bumper.
Another spinoff idea that i havent got round to making yet is to use the same principal to rake the pins.
I havent managed to rake one open yet, but you can rake enough to set half of the pins, then retract the key and begin picking the rest.
Im not sure how these ideas would work on non-dimple locks though due to the orientation of the key
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As for your tension problem, wouldn't it have been easier to put a length of wire or wiper insert through the hole in the key bow instead of all that filing? 
