My new bike has a 12-27T rear cassette. I want to ride single track....climb any hill and perhaps xc race eventually. It is a Ti HT. My front gears are 22/32/44T. I ordered a larger rear cassette (11-34T) to accommodate my desire to climb. I read an article on chain length regarding advantages of running a shorter chain. The Ideal Chain length for my current setup (27T rear)...according to the calculator is 53 inches or 53 lengths (2 pieces make a length i guess). The calculator suggests a 55 inch chain with the larger, 34 rear cog.

The article I read says that a shorter chain will prevent me from shifting into the larger rear cogs while in the largest front gear but the smaller chain will make for:

Crisper, faster, more reliable shifting.
Can use a shorter rear derailleur cage.
Less chance of over shifting (changing two gears when you only clicked one gear at the shifter).
Less chain slap.
Less chain weight.

The article suggests using your middle front gear to determine your chain length in this set up. According to that calculation, with the larger rear cassette and using the small chain theory, the calculator puts the suggested chain length at 51 inches. That being the case, I am going to try to use the existing chain with my larger rear cassette.

Anyone out there with personal experience to tell me that this is a bad idea? I know that I will have to look at it but I am worried about breaking my chain, derailleur, hanger, etc.

For determining chain length I shift to the big chain wheel and biggest cog and shorten as much as possible without the chain going straight as it passes through the deraileur.

Parker's site has some good instruction on this.
https://www.parktool.com/repair/readhowto.asp?id=26

If you value the rear of your drivetrain, size your chain by running it tight from big chainring to big cog(forego derailers for sizing) and add one extra length. The advantages of the other mentioned method are outweighed by the catastrophic failure when you accidentally cross over big-big while riding.