A lot of people shoot it at 200 normally, don't they? I know the slower Efke emulsions are often uprated by a stop. So it may be more like a 3-stop push---which is still, however, pretty extreme. IMHO, what you want to do is develop the film to completion while keeping fog as low as possible.

Donald Qualls's "Super Soup" recipe---basically it's HC-110 dil A mixed with Dektol stock in place of water, plus some ascorbic acid and washing soda---does this quite well with faster films, but I've never tried it with a slower single-layer film and I have no idea what would happen.

If the roll in question is of any importance, I think you should do a test roll first with whatever developing regime you want to go with.

-NT