Not a lot of price difference between 24/27 group but you are picking up ~20 amp hours so it is probably worth it if the larger battery
will fit in the location.
If you ever go solar
that "extra" storage capacity will come in handy if it is not sunny for a couple of days. Or even just figuring an extra 8 - 10 hrs. of running that fan if it's hot.
I know an earlier post mentioned that a pair of 6 volts (being 120 lbs. of battery) will have a lot of amp hours. 120 lbs. of 12 volt would be pretty close to the same. However 6 volt batteries for golf carts etc. are "true" deep cycle batteries, designed to withstand deeper discharge better than "marine" or dual use starting/deep cycle. True deep cycle also tend to do better at sustained load. If you need 225 ah it will certainly provide it. With one weakness if either battery malfunctions you don't have 12 volts. Which is why some earlier posts mentioned going to dual 12 volt batteries. Slightly less amp hours but either battery can run the system on it's own, just with less capacity.