I'm not sure how applicable this is to GA but low turns in gliders are discussed here..
http://www.abqsoaring.org/misc_files..._Accidents.pdf
Basically the message appears to be not to float around the turn slowly trying to preserve height but the get the turn done positively. A slow turn has a larger radius, longer distance to fly therefore potentially a greater loss of height. I don't believe this contradict the advice to fly the turn "just above the stall" because the stall speed will vary with rate of turn.
See page 15..
"A common mistake by many glider pilots in situations when height becomes critical is to instinctively keep the glider’s nose up while entering a dangerous low-banked turn with the intention of preserving height. Knowing that at the same rate of lift while circling in a thermal, a lower bank angle will increase the rate of climb the pilot assumes that a lower bank angle in a no lift situation will preserve height due to the lower sink rate. This can be a fatal mistake. As demonstrated above a low-banked turn takes much longer to complete and as a result significantly extends the glider’s exposure to its inherent sink rate. This leads to a higher total loss of height despite the lower inherent sink rate as compared to a high-banked turn with its relatively higher inherent sink rate."
continues..