If you're looking at the Speed Passion, I'd recommend looking instead at the Hobbywing Xerun. It's the same speedo, but with different casing. Hobbywing make the Speed Passion.
For a 2wd, you'd probably get away with the 60A version (same as the SP LPF), but as they are so cheap in comparison, you may as well get the 120A (same as the SP Pro).
You can get them cheapest on ebay from China, but if you want the peace of mind of buying from a UK supplier, have a look at
RacersInExile <<<click.
Even with the programming card (which is helpful to access all the settings) they are cheaper than the SP (which will still need the exact same programming card).
I was gonna say this when I first saw your your post, but assumed RogerM would be along soon to sing Hobbywing's praises
. He must be on holiday or something.