HP EliteBook 840 G5 Notebook thunderbolt 3  

@mehenn It has a Thunderbolt 3 port but only 2 PCIe lanes. The good news is you may use the NVMe M.2 slot inside for better eGPU performance. @Nando4 has built one and it posted impressive numbers. If you prefer Thunderbolt 3 connection for convenience and power delivery, I'd recommend going with the HP EliteBook 840 G6.

@itsage

Thank you!  How portable will be with the M2 connector? Won't that be sticking out of the bottom of the case prone to tearing up?

@mehenn , Elitebook 840 G5/G6 are very nice laptops.  If getting the FHD non-touch version, look for the automatic light sensor (ALS). System equipped with the ALS come with the 400nit LCD, rather than the non-ALS 220nit LCDs.

For eGPU use, my 840 G5 with a M.2 egpu was very fast, eg:

https://egpu.io/forums/pc-gaming/forza-4-benchmarks/#post-53800

Problem there is the system only has one M.2 slot.  Theoretically, the SSD could be swapped in/out but given the value of data, it's hardly practical. The better solution is to use the WWAN slot to host a x1 2242 SSD as discussed, liberating the x4 3.0 M.2 slot for eGPU use. Or use a TB3 eGPU.

Some other pointers:

- HP's recent BIOS disables undervolting You'll want to rollback to an older BIOS if wish to unlock undervolting and increase TDP.

- the dGPU model has a beefier heatsink, useful if undervolting/TDP unlocking and wanting to turbo the the highest multiplier without temp throttling

- 840 G5 has  a 2-lane TB3 port due to the Kaby Lake CPUs having only a total of 12-PCIe lanes.

- 840 G6's Wiskey Lake CPUs have 16-PCIe lanes. HP could now have a 4-lane TB3 port but couldn't find verification of it anywhere.