Based on my experience CPU consumption is not much more.
In the past I had also the "suspicion" it has to be a PCIe card.
Therefore I build afterwards a construct like this, to use the UFX as preamp on a RayDAT.
https://www.tonstudio-forum.de/blog/ind … RME-RayDAT

If you compare RME PCIe, FW, USB, thunderbolt solutions in terms of RTT between PC and recording interface,
then you will notice, that USB and Firewire are very close to PCIe/Thunderbolt based solutions:

If you create very big test projects with 400 tracks (!) and 2 VSTs per track (!), then you will notice,
that with the UFX+ via USB3 you can still playback with only 32 samples ASIO buffersize without pops and clicks.
See my blog article: https://www.tonstudio-forum.de/blog/ind … acks-de-en

In smaller projects with 2-3 VST instruments (Superior Drummer, Trillian, B4) I tried to find out whats better,
UFX or UFX in front of a RayDAT in terms of CPU, but tbh I couldn't find much visible difference.

I leave it up to you, whether you still want/prefer a PCIe based card.

I would rather than that suggestion to look at the UFX II. Then you have a real top recording interface with so many advantages. And as it is a 30 channel interface it still fits to USB2 which makes this very flexible.

I recommend the UFX II because it is the UFX+ (minus MADI, minus Thunderbolt) that has been designed last recently and hast latest converter technology, overworked preamps, analog section, better headphone outputs, better Durec, timestamps in Durec recordings, additional features to make standalone operation more complete, you can connect the ARC USB directly to the device which is nice for standalone operation.

If money is not limiting you, get UFX II. Otherwise look at UCX.
802 needs the old ARC to switch between standalone profiles and doesnt have auto set.

Look at this comparison sheet in my blog article:
https://www.tonstudio-forum.de/index.ph … 017-12-pdf

So my recommendation to you is, don't limit yourself (in terms of interface selection) too much because "you heard" that USB might be a disadvantage because of higher CPU consumption. Get the recording interface that covers your current and future demand. Recording interfaces that have been designed last recently usually have the latest converter technology, analog section, phones preamps. And look at the final cost, the AIO becomes quite expensive if you expand it to the full solution when buying each available module. Also I regard it as better to have 1 big USB cable from PC to rack instead of having to deal with breakout cables in the back of the PC.
And build your setup simple in terms of the number of TotalMix FX instances that are required to manage your setup.

If you use i.e. an UFX as Preamp and for AD/DA in Front of your RayDAT (like I did for some time), then you need to control the routing for each of the 2 Recording interfaces in 2 separate TotalMix Instances. Possible and can be easily hardcoded, but this is not everybodies taste. When connecting only pure Preamps or ADDA devices, this would not occurr, since you control the routing then exclusively on the RayDAT card.

The most flexible solution is to use RME recording interfaces together with the Octamic XTC, which can be configured as an AUX device, so that you can control the most required functions of this very versatile Unit via the one TM FX instance of your main interface (be it an UFX* or RayDAT or whatever). You only need MIDI cables for the remote control of the XTC. And even this can be topped if you would get i.e. an UFX+ which supports MIDI over MADI. Then you have 1 fibre cable, you can connect up to 8 XTC and build a fiber ring between these devices, where each cable maybe be up to 2km long and the you can remote controll all the 8 XTCs from the one TM FX instance of the UFX+, which makes the UFX+ with MADI to a very versatile unit. Octamic XTC also comes with MADI. And there are several other interesting preamps and AD/DA available to expand this solution further. Most versatile is the XTC and much comfort as you can control everything in the TM FX instance of the UFX+. Ok .. everything has its price, its not cheap, but very flexible, the only reason why I told you this, as not many people know about these advantages when using MADI.

Another nice feature of the new devices like UFX II and UFX+ is, that the MADIface driver supports many devices.
This means that ALL devices which you connect by MADIface driver can directly be accessed by your DAW or other application that supports ASIO, as of now you can access by this one driver these devices: UFX+, UFX II, MADIface XT / Pro / USB, OctaMic XTC, ADI-2 Pro, Digiface USB.

to 1) I think you can deduce it from this link https://en.wikipedia.org/wiki/Thunderbolt_(interface)

to 2) don't know why you ask this .. look .. you might know that all the channels of UFX+ are transferred instantly. There simply needs to be enough bandwidth to transfer them. USB3 (which is also full duplex) is able to handle the bandwidth of all UFX+ channels, thus thunderbolt also is capable of handling it.

USB2 bandwidth 480 Mbps (half-duplex) was alway sufficient to transfer 30 inputs and outputs (UFX, UFXII)
USB3 bandwidth 5000 Mbps (full-duplex) is sufficient to transfer 94 inputs and outputs (UFX+)
Thunderbolt     = 2 x 10.000 Mbps multiplexed
Thunderbolt 2  = 20.000 Mbps 1 logical channel
Thunderbolt 3  = 40.000 Mbps, I assume also here 1 logical channel

USB3 has approx 10 times the bandwidth of USB2 and is full-duplex. But the UFX+ has not 10 times the amount of channels, so USB3 should be fully sufficient to transfer all channels of the UFX+.

Thunderbolt is 4 -8 times the BW of USB3, so the BW for UFX+ is much much more than sufficient.