Think I would need that big of one even if I don't run a TL?
If you have a completely stock ski, and you run a 260 CCA battery, you're reducing your battery cranking power by 20%. That's not a good idea. Yamaha designed it with 325 CCA for a reason. That said, people run smaller lead acid batteries with no issues (Etx- 9, Etx- 12, etc). Keep in mind the lower the CCA, the harder you work the battery. Buying a lithium that's smaller than needed puts additional stress on it, shortens its life, and increases the risk of failure.
Lithiums are best suited for TL applications, as they are designed to be run down and recharged. Lead acids are not. The additional static voltage (ocv) of the Lithiums adds a bit of power (electrical), and reduces starter/starter relay wear/failures.
The added CCA available in batteries such as the AG 16 cell (480) and the AG 20 cell (600) is critical when you step up to big CC motors and high compression, as is proper cables and connections.
On a stock type setup, benefits are questionable (other than weight). These batteries shine on big CC, high compression, TL setups.