This is my understanding of the differences
About 6K if bought from Ralliart UK
GSR has ABS and AYC, RSX does not
RSX has no warranty, GSR has 3 year warranty if bought from Ralliart
RSX has quicker steering rack
RSX probably the quicker straight line car due to lack of ABS and AYC to weigh it down
RSX only available in White.
Hope this helps.