USB Type-C speed with USB A port?
Here needs to be a small clarification. The compliance to USB 3.1 standard can mean anything, even a mouse can be declared "USB 3.1", because 3.1 includes all modes for USB 3.0, which means USB 2.0 at high-speed, full-speed and low-speed modes. However, when seeing "USB 3.1", most people would assume that the interface will give them speeds at 10 Gbps rate, so-called Gen2 speed. 

Unfortunately, up do date (Sept. 2017) there are very few peripheral devices that work at Gen.2 speeds. While there are some pilot reviews of Gen.2 flash drives, very few are practically available to public, practically none. The only device known to me is the USB-SATA bridge (found in USB enclosures) based on ASMedia ASM1351 Gen.2 chip.

Therefore, even if the Macbook does have the USB 3.1 Gen.2 capability, there is not much you can get out of this. 

To use your legacy "3.1" peripherals with Type-C port you can use either "legacy cable assemblies" (Type-C to micro-B cables), or use an adapter. Adapting Type-C to legacy Type-A requires only passive wire connections. I would strongly suggest to use "mini-adapters", since they are based on a single small PCB between Type-C and Type-A, and don't involve hand-soldered cables. These mini-adapters should have much better chance to support Gen.2 speeds, if you have it. Still some experimentation will be required to see if these adapters work at Gen.2 speeds, people do very weird things in these simple devices.