RIMS Step mashing- no direct fire

I have a newly built sabco clone and I opted to not install a direct fire burner. Here is the riddle:

I want to make a DFH 90min clone using greater than 90% pilsner malt, with a 122/149 step mash. With my current system (1500 watt element/1330 watts actual) the temp rise through the heatex would be about 9 degF @ 1gpm. with a mash thickness of 1.25 qt/lb with 20% grain absorbtion I would be circulating roughly 9.25 gallons through the tun.

circulating that volume I would raise the temperature in the tun 9 degrees every 9.25 minutes- and with a desired rise of 27 (149-122) it would take 27.5 minutes to raise the temp to 149. some people say that taking that long to raise the temp might cause some HSA, others say no problem. what say you HBT?

Also- should I not include the time it takes to raise the temp into the mash profile? 20 mins @ 122, then 30 to increase the temp to 149, then just go until conversion is complete?

If you don't splash the wort while it is going back into the tun I would not think that it would cause a problem.