The NVIDIA thing has been answered elsewhere in the thread, so I'll answer the other one: ... It depends, but usually there's a minor performance hit. Other times it works just as well, and there are some edge cases where it actually works better.

There's also the issue of compatibility: in general, if anti-cheat software is involved, expect to have problems. This website is a database for Steam games with reports from users about what works, what doesn't work, and what can be done to fix or at least mitigate what doesn't work. You can sync your Steam library to it to see how well the games you have are supported at a glance.

World of Tanks. Came for the fun FPS/TPS hybrid gameplay, left for Wargaming's unforgivably greedy and short-sighted monetization practices. But not before siphoning away a lot more of my time than they deserved before I caught on.

So, is that an order to abandon ship?

Start from Doom. Well, not quite the original release, but rather Doom Legacy. From this base, create a 3D Sonic platformer styled after the Genesis era games. That's Sonic Robo Blast 2 (because yes, it's a sequel from a previous fangame named Sonic Robo Blast from all the way back in 1997).

We're not done yet. Mod it further... into an online kart game. That inherits the same modding abilities Doom Legacy has. You've got Sonic Robo Blast 2 Kart, sometimes nicknamed MUGEN Kart to the dismay of its developers due to the sheer amount of addons for increasingly weird characters its forum hosts. If you're interested, said forum, hosting both the addons for SRB2, SRB2 Kart and the SRB2 Kart releases themselves can be found here (for some reason the main website is down as I'm writing this. Oops.)

For SRB2 Kart in particular, the thread to get your hands on it is here and you can find its repository here.

The game is wacky, very fun, runs on a stale potato and it's easy to set up a server to subject an unsuspecting community to your specific choice of insane mods among the hundreds if not thousands available.