Local network - wireless is faster for some reason?

[Andi]

If everything is connected to the Gigabit capable switch
Then 1000 Mbit things will go at 1Gbit
The router will connect at 100Mbit also (it will not slow the Gbit things down)

The point of a switch, is not to share everything will everthing like a wire...
but to only connect the one thing to the other thing that needs to be connected to.
There is no waiting for the slowest traffic.

Switch - think (multiple) flyover connections between devices
Hub - think crossroads, and yes everything needs to wait to clear the junction.

So if you have no other traffic,
then 2 Gigabit devcies will happily talk to each other at 1Gbit
and if another (or even one of those) needs to talk to the 100Mb device it can for those packets only.
The Switch buffers everything, so it does not matter if things are at different speeds also.

That the router will not go faster than 100Mbs will not matter at all, if it connects onwards at less than 100mbs (even Fibre internet is only 79Mbs at best), so no benefit to increase.

as for wifi, think 30% throughput at best of whatever is quoted...
it is very much a HUB device, and has a single channel (not 2 way comms) to handshake the packets accross the wifi channel.. so 100Mbs through on a 300Mbs connected link.