My answer may be 'non-typical', because here in the UK, probably over 50% of cartridges are 2 1/2" (I'm talking 12 bore).

I always shoot 2 1/2" cartridges - even in my guns that have 2 3/4 " chambers (i.e. AyA, Beretta, and Merkel). All of my English guns are chambered for 2 1/2" and I would not put a 2 3/4 through these guns. Low pressure may be safe, but if there was an accident, insurance cover I have would be invalid, since in the UK cartridge cartons are marked with the minimum (CIP) chamber length.