I only use 750ml champagne bottles. Never had a problem with pasteurizing, they're rated for much higher internal pressures than beer bottles.
I pasteurize in a canning pot with wire rack to keep the bottles off the bottom. Set starting water temp to 160, then add 6 bottles, and start the timer for 15 minutes, stirring occasionally for even heating. Temps drop about 10 degrees then rise slowly. Close to 160 again when the timer chimes.
No bombs ever, but I always track carbonation with a plastic soda bottle, then measure the SG drop and test for over-carbonation by popping a glass bottle then re-cap and proceed.
I also wear safety glasses and sleeves/pants/footwear when pasteurizing. Safety first. If a champagne bottle fails due to pressure it's pretty spectacular. Seen people get cut by flying shards of glass a few inches across at ~20ft. Not something you what to have happen in your kitchen.