EDIT- I figured ot the issue, this
bike does have Sora ST-3503 levers on it which are "New Super SLR" which have increased cable pull and "can be used with "Super SLR" (less cable pull) calipers", but the result will of course be reduced caliper force for any given amount of force at the lever, so getting some new calipers that are "New Super SLR" is the way forward here. If one wanted to make a very powerful brake system they could use NEW SUPER SLR calipers with SUPER SLR levers, but the pads will not back away from the rim all that much, and there could be issues with the brake lever hitting the bar, but I doubt it.
My girlfriend just picked up a 1997 Klein Quantum Race, it has some shimano 600 dual pivot brakes on it and the springs seems quite stiff, they "work fine for me", but her hands are certainly smaller than mine and not as strong and on longer descents her hands get quite fatigued. When I initially test rode the bike the stiff springs actually caught my attention, but I didn't think too much of it, but, they are a bit of an issue.
The bike is kept up well, and there isn't any drag in the cable housings, the levers are Sora as the original Ultegra levers on the bike had worn out and were replaced.
It seems I could remove the brake and tweak/bend the spring a bit to reduce its efforts to keep the brake open? Or has anyone else addressed this issue before?
Here are a couple pics,
