I used to race the 710 long time ago if i remember correctly the 710 are fast if you dial it in and dialing it in is a little hard because the sweet spot on these car's are a little smaller .. for that price you can get a good newer roller ... the 747 are a nice, just drove one couple of weeks ago and i was amazed how smooth and easy it was to drive ...
as to your question is it old yes its outdated.. the car geometry has improve so much that the 710 would be hard to set up compared to newer cars, parts are also hard to come by
400 a little to much for a 710 nowadays.. i just sold a xray nt1 2011 for 250 perfect condition too..