Actually, the multiplier doesn't require any faster shutter speed than the same focal length lens on a film body. The amount of image movement with handheld shaking is the same on the CCD as it is on film. The image area the lens normally covers is cropped, not magnified. The rule-of-thumb minimum reciprocal of 1/80 for 80mm should work just as well (or poorly) on film and digital.
That said, a fast enough shutter speed or tripod support would be one thing to do. The other is to realize the relatively shallow depth of field if the shooting is done at wider apertures. Try a few tripod supported shots at f/8 or so and see if the sharpness is still a problem. The 28-70 will be more forgiving of both shutter speed and depth of field. This isn't a digital vs. film body issue.
I thought about this longer I take back what I wrote above about the magnification factor. The image movement on the CCD is identical to the movement on film, but to make a print of a given size the smaller CCD image will have to be enlarged more. Therefore blurring due to lens movement will be enlarged at the back end of the process. So yes, a cropping DSLR would require a faster minimum shutter speed. This stuff gives me a headache sometimes.