The better choice for the ECX Ruckus would be a brushless system from the Losi Mini 8ight or a brushless motor called the "Ammo" from Great Planes paired with a HobbyKing 60amp Mini ESC. I believe you can get a 3900kv motor to replace that 370-380 size motor. Part no. for the Ammo motor is GPMG5200 from Great Planes. Losi also has a Lipo option part #LOSB9835 for 2s or LOSB9836 for 3s output from the Losi site.

the mamba micro system works well for the mini-t platform and the associated rc18 platform but they are quite small compared to the 1/18 Ruckus which is about the same size as the Dromida SCT 1/18. Dromida has a brushless kit that includes:

FEATURES: Upgrades stock 370 size brushed motor supplied with Dromida 1/18
scale vehicles
All components required for brushless operation

INCLUDES: 25A Brushless ESC, DIDM1002
12T Pinion for the MT4.18, DIDC1032
13T Pinion for the BX4.18, and SC4.18, DIDC1115
5300kV Brushless Motor, DIDC1128
Brushless Conversion Receiver, DIDL1000
Brushless Bellcrank Set, DIDC1130
Brushless Steering Linkage, DIDC1129
Brushless Servo Mount, DIDC1131
2.5x6mm Socket Head Screws, DIDC1132

Hope this helps your speed cravings. So is this a smart thing to do? Well hind site is always better then foresight. If you got the money go for it.