To maintain at least 1.2 above stall at a 60 or 89 degree turn would require significantly increased airspeed over Vx or Vy. The push forward to achieve this speed will require loss of altitude until this margin is achieved (straight ahead or in a bank).
I think the 45 degree recommendation is based the more rapid (and less complex) transition from Vx to 1.2-1.2 over stall at 45 (varies by airplane, but will be pretty close IIRC in a C172/C205/6, A36, 35 series).
You're not going for 1.2 above stall, you're going for right AT stall. Increasing the speed from 1.0 Vs to 1.2 Vs increases the turn radius and the distance flown in the turn by 44%.
Here's a few screen shots from a spreadsheet I made. This table calculates load factor and turn radius (actually, turn diameter, this is how much room laterally you need to turn around, handy for knowing in a canyon type of situation) for a selected airspeed, Vs and 1.2Vs at the given bank angle:
Here, at 45 degrees bank, notice that 1.2Vs is 81 knots.
Notice that here, at 60 degrees bank, Vs is 81 knots. Now, notice the difference in the turn radius between 45 degrees/81 knots (1.2Vs) and 60 degrees/81 knots (Vs): 587 feet vs. 333 feet. That's a HUGE difference.
Here it is for 74 degrees of bank, which is as far as you can go within normal category limits:
And 76 degrees, the limit to stay within utility category:
That doesn't buy you much! Now, just for fun, here it is for 89 degrees of bank. Notice the load factor and the stall speed!
Notice also, that it doesn't gain you much of an improvement in the turn radius over the previous couple.
Finally, here's the table I originally started with. It's calculating the diameter of the turn for a range of airspeeds and bank angles. The red portion is where the airplane would stall.
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