I concur with what was written above. The PSR-E463 is LIGHTYEARS ahead of the PSR-275, based on what I see in the manual for the 275. The 275 might be a fine, basic keyboard to learn on, but the E463 has tons more features. The registrations were mentioned above, and to me, that is an extremely important function for live playing. On the 275, you can set up a pretty complex sound using the main voice, dual voice, split voice, as well as chorus, reverb, and harmony settings. But then once you set up a sound you like, there is no way to store all of those settings so that you can easily recall them. But on the E463, you have a total of 32 different registration memories that you can use to store and immediately recall these settings.
It is important to note that some other Yamaha keyboards of the late 1990's and into the 2000's had registrations, but only had two registration buttons immediately available (additional registrations were accessed by using another button to select different banks of registrations). Only having one-touch access to two registrations was, in my opinion, also pretty limiting, as you might want to quickly change among several sound set-ups while playing a song. But about a decade ago, Yamaha finally went back to supplying 4 direct registration buttons in this type of keyboard, and this includes the E463.
Beyond all of this, the E463 includes synthesizer-like features like filter cutoff, resonance, envelope generator, digital signal processing (for a variety of additional effects like phase shifter and rotary speaker) and sampling. The E463 also includes a 6-track sequencer and the ability to save your sounds and settings on a USB flash drive.
As for the EZ-play "single finger" chords, as far as I can tell by looking at the manual to the PSR-275, this feature is nearly identical on both keyboards.
So, yeah, given a choice, I would definitely keep the E463 over the 275. Or, if you really want to have fun, you can set both of them up like an organ, with the E463 as the top keyboard, and the 275 as you lower keyboard. Doing this would allow you to really orchestrate your sounds during a song by not only being able to switch between different registrations on the E463, but to also have another sound set up to use at the same time on your 275.