The RX1 was a 4 cylinder carbd sled. In 06 when they went to the Apex, EFI was introduced. The chassis on an Apex vs an RX1 to me is a big difference. I prefer the forward handlebars of the Apex chassis vs RX1 chassis. With that said the RX1 was a good sled and can be picked up for cheap. Motors are reliable as well. You could always add a pivot riser if needed.
I do love the Yamaha 4storks though.