Ninja edit: I guess you're suggesting that some parts are in hand rolled x86 assembly, not just pure C++ that would be output as the cross compiler target architecture?
Performance? Who knows.
Plus another 100 or 200 in adapters. It's beyond me why they would make a laptop with zero USB and zero HDMI ports.
Total is $2000 when converted back in USD.
The 10% might still be to account for the instability of the GBP.
However it still won't give you any HDMI or audio or Ethernet output. If you try to get one more adapter, say HDMI to connect a projector, you won't be able to plug it because there was only one thunderbolt port in the first place.
£75 pounds for basic connectivity https://www.apple.com/uk/shop/product/MUF82ZM/A/usb-c-digita...
£120 pounds for dual display with dual USB. https://www.apple.com/uk/shop/product/HMX02ZM/A/caldigit-thu...
£230 for a dock https://www.apple.com/uk/shop/product/HMX12Z/A/caldigit-ts3-...
That said, it sounds like you're really not interested in this market and I recommend you look elsewhere for a solution.
https://www.amazon.com/Anker-Upgraded-Delivery-Pixelbook-A83...
https://www.amazon.com/Anker-PowerExpand-Adapter-Delivery-Et...
Games are mostly C++, based on my experience with C++ codebases I'd say there's about zero chance that a game could be (easily) recompiled and made to work on ARM.
And games won't be ported anyway because it's too much work for too little sales, even if a developer really wanted to make it work they'd need a $2000 new mac to be able to compile/test in the first place.