If the PC only has 8bit slots chances are that it's an XT, AT machines could already have 16 bit slots.
I don't think that performance will matter very much since the 8088/8086 CPU won't be able to saturate the card. And most VGA games probably won't run very fast on an XT.
I would instead go for something with good CGA compatibility. I think some early Paradise cards might be a good choice.

If the machine is an AT or higher I suppose it will be slowed down if you use an 8bit VGA card, regardless which model.

Problem is finding an CGA monitor, I never saw one once here.

Some Commodore monitors support CGA. Alternatively, it's possible to make a CGA->SCART cable.

For native 8-bit I think the cards based on the Paradise PVGA1K are pretty good in terms of performance and compatibility. Remember you can also use a lot of 16-bit cards in 8-bit slots.

Usually Trident VGA graphic cards have jumpers for 8-bit compatibility.

I didn't mean to use a CGA monitor, but a VGA card which offers good CGA compatibility from a software point of view. See CGA Compatibility Tester vs. VGA cards

I use an ATI VGA Wonder XL. It's a 16-bit card, but it works in an 8-bit slot. The image quality and speed were both improved on over the VGA Wonder 16. I would think Cirrus or Trident cards would also work well.

I also use ATI VGA Wonder XL 512k in my XT`s. With the included software i can set the ROM to 8-bit mode instead.. And these ATIs have a great backward compatibillity.. So i can set the card with the included software to each MDA, CGA, EGA, VGA mode i want.. And that with a regular VGA monitor connected to the graphics card.. It also haves a Bus mouse connector too.. So those i use to give my XT machines an mouse with higer DPI.

Oak cards (the ones with 512KB max RAM, two display ports -TTL/analog- , and a configuration switch) are definitely work in 8-bit slots. They also can emulate MDA, CGA, and EGA, as well as VGA. There are also several 8-bit Genoa (EGA) and Paradise (EGA, VGA) cards available at the moment around ebay, though they are a bit pricey.

Cool, thanks for all the info 😀
It is definitely funny to see an 16bit card in an 8bit slot 😁
I will know more once it arrives (tomorrow hopefully).

Its an Phillips NMS9100 computer, with Western Digital 30 addon card and harddrive (probably dead, but i have two more), and an parallel interface or sometihng.
I am currently cleaning it up.

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Cool 😁
I am currently cleaning it, the motherboard is pretty much flawless, only there is some hard duse near hte connectors.
The thing that needs a bath is the housing, its dirty as dirt.

Do you know about upgradeing this computer? It has an Intel 8088-2, no CO-Processor.
Here is an image of the board: http://i.imgur.com/1qOlHsU.jpg

Does it run at 4.77MHz, or at least offers this speed? In that case I would leave the CPU as it is for full speed compatibility with IBM PC. Otherwise you could replace the 8088 with a NEC V20 for a small boost.
It will still be too slow for a lot of EGA games, let alone VGA. Early Sierra adventures (AGI) might run OK in EGA mode, later ones (SCI) not. My family used to have an XT-Clone with an 8MHz 8086 which would be faster than most 8088's (I don't know how fast you'd have to clock an 8088, maybe at 12MHz it would match an 8MHz 8086.) That's why I suggest to get a VGA card with good CGA compatibility, games that support EGA should run fine with faster machines like 286 or 386. You'll still have the option to use a VGA monitor and run EGA or VGA games or early GUI's if you want to try.

Forget about the FPU, not relevant for games until much later (see previous discussions, very few games for 386 would profit from an FPU, that started with Pentium).