Everything I've ever heard says that root development coincides with shoot development... In other words there would be no be benefit to topping them.

i have a question for you though, how exactly did you propagate by cuttings? I tried once unsuccessfully and most everything on raspberry propagation only talks about division for increase of plants. I would love to take cuttings though.

I'm not sure what type raspberry it is, I do survey work on foreclosed lots and I found this mother plant this spring and transplanted it to my yard. It's growing like crazy, lots of trailing laterals and the berries are a deep red (Zone 7b). I just cut the last 5" or so from each lateral and put them in a 25/75 mix of peat / perlite after dipping them in a rooting hormone. I put the cups in the shade and only watered them when the mix looked dry, I sprayed the leaves as much as I could with water and within 2 weeks I had roots. This is the only raspberry plant I've had luck with propagating, I think the actively growing trailing raspberries root quicker then the erect kinds.

I have some erect thornless blackberries I also found, all the cuttings rotted in a 50 peat / 50 perlite mix so I decided to try only perlite. I cut 6" sections of the blackberry cain and left at least 1 leaf on the cain, dipped them in rooting hormone and put in the cup of watered down perlite, I then put them in a tote with the lid on and put it in a shady area watering them 1 time a week and sprayed with water if needed to keep the leaves damp, I have no rot yet and It's been 2 weeks, I took 1 of the cains out today and seen a really tiny root starting at the cut end but still have a way to go, I think the perlite might be the way to go for blackberries to prevent rot, the thicker part of the cain seems to do better than the tips also.

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Let them grow naturally....prune the shot only when dormant