Quite possible that Fifa 99 doesn't recognize the V5, as I'm not even sure it recognizes the Banshee out of the box. Was there a Voodoo3 patch for Fifa 99? If so, applying that might make it work with your Voodoo5. You may also try earlier drivers.
To answer your question in the OP though, I believe World Cup 98 is strictly 640x480, but it's been a while since I last tried. Fifa 98 is locked in that resolution for sure, I'm willing to bet World Cup is like that as well.
Fifa 99 does allow you to hit 1024x768 with V2 SLI, which you can't do with a single card obviously. Whether or not that is something that's worth the prices of Voodoo 2 cards in this day and age is something you'll have to decide for yourself. I personally wouldn't get one for slightly higher res in a football game, but there's definitely a coolness factor attached to owning a Voodoo2 SLI setup.
I personally use CRTs for old systems and as such prefer lower resolutions and greater performance. Paired with a fast CPU, a single Voodoo 2 is fantastic at 640x480, at 8x6 it can chug badly sometimes due to fillrate or memory thrashing. Same applies with V2 SLI and in fact can be even worse at 1024x768, where as at 800x600 I tend to prefer the performance. As such, I tend to agree with leileilol, although the Banshee is a very slow card, the Voodoo 3 offers higher performance and far superior image quality, as Voodoo 2 can be pretty noisy and SLI looks pretty funky, but hey some people really dig that and that's fine!
It's really up to you.