Both those applications are extremely susceptible to pack loss and delay. If you look though the questions on this forum the vast majority are people complaining about slow wireless which is almost always due to interference which cannot really be fixed.
So now if your only option is wireless then you get to the next issues.
It is the combination of both the router and the card in your machine that determine the connection. Buying a high end card for your machine and using a cheap router or the reverse only runs as good as the lowest device.
So you need to look for the "best" card that matches your current router feature set.
In general PCI cards main problem is the antenna are located very close to the case and are blocked to a point. If the backside of the case faces the router it does not matter but if you stick in against a wall you lose a lot of your signal. There are some PCI card that have antenna extensions...some of the so called gaming one do...that let you move the antenna from in back of the case. The problem with antenna extensions is that the longer the cable the more signal loss you have. Even though they place larger antenna on the ends of the cable many times the total signal getting to the card is actually less.
So as you can see it is not really a easy question...other than not to do it in the first place.
What's the best PCIe wireless card for gaming and hd streaming?
PCIE wireless cards are nothing but headaches. I've went through 3 with nothing but issues. Just get a wireless router that can run DD-WRT. Wireless routers have better signals than just regular wireless access points. I had a netgear router I turned into an access point and never had any problems. Of course if you want a PCIE wireless card. I've heard good things about mini-PCIE laptop wireless cards that some people have just used a Mini PCI-E to PCI-E adaptor to connect to their desktops. Laptop wireless cards are better and cheaper.