YoungChazz runs a nice board at www.4wdrc.com
that has info on the various 4wd vehicle offerings including his X-5 which is quite the handler and is a nice upgrade to the XX-4 platform.
The Academy SB Sport needs only a few upgrades to make it quite competitive, with a Sport with upgrades making the A-main at the stock nationals.
The vehicle can be purchased in the USA from your LHS ( have them contact MRC to order ), direct from MRC, or from www.ultimatehobbies.com
but you must call them as they don't list it on there site.
Last time I checked, they sell the SB Sport for $145 and the SB Pro for $225, right now with free shipping.
For the SB Sport, you would most likely want to upgrade to alloy shocks, weather the Academy brand replacements or a set of Team Associated B4 shocks all around works quite well.
B3 Lunsford Titanium turnbuckle kit is what you want to replace the kit thread rods.
If you have more questions, feel free to email me specifically what you would like to know and also visit www.rc10b4.com
and in the General section is a thread that has many MRC / Academy Drivers as well as team drivers and MRC representatives posting as well.