It will be worse, I assure you. Just because the USB drive is solid state as compared to a hard disk doesn't mean it's faster. The USB interface is much slower than SATA.
Personally, I run MWO off an external Firewire hard disk on my secondary machine. It's an i7-950, GTX 570, 6GB 1600 build, so computational power is not an issue, but it does take ages to load maps. So much so, that sometimes the match has already begun by the time my client gets with the program. However, once everything has loaded in, it runs fine on Very High at about 50 FPS, adaptive vsync.
The reason the game is on that hard disk is because the internal one is only 160GB and 9 years old. I kinda cobbled it together from spare parts. :L
Edited by ThatBum42, 08 April 2014 - 01:18 AM.