I don't feel that 2wd SCT needs a 550 motor. Even a 4wd SCT is ok with a 540 motor. Speedos that works best for 1/10 SCT to me at Speed Passion, Hobbywing, Tekin..etc 1/10 speedos. Just found another great speedo, it's exactly like a Hobbywing Xerun 120a and Speed Passion GT 2.0 pro but the components inside are really good. Uses Toshiba FETs. It's really cheap as chips as well. Comes with the 80a and 120a models, i'd go with the 120a model. Try it, you guys won't be disappointed...
http://www.brushlesshobbies.com/
http://www.brushlesshobbies.com/120A...mer_p_113.html
These speedos have pop up on Ebay as well, but i rather get from the store linked above, at least when the speedo is faulty, you can inform and get back to the shop and the owner Stan is a great guy to deal with.