I don't exactly know what are your tastes in vidya, but the Steam Deck OLED should be convenient to you assuming you primarily stick to Steam and aren't picky about graphic fidelity and framerate. I made some benchmark clips (through my capture card) to give you an idea what the overall performance is like on demanding Japanese games.
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On the base PS4, this mission in particular runs at a constant 5~15fps.
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Some specific zones that contain a large amount of foliage and background details, such as the eastern gate of Raya Lucaria, will cause the framerate to go a bit below 30fps (which was put as a limiter for this game from the Deck settings).
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Bear in mind this is the base Deck model, so the OLED should give a small bump of performance as Digital Foundry pointed out in their own tests.
On retro emulation like PCSX2 or PPSSPP, the battery life of the base model can already stand up 5~6 hours from a full charge, an extra hour or two with the wifi disabled.