The RX-1 is BASICALLY nothing more than the current RX-2 with a stock change. The RX-1 has a beech stock where the RX-2 is a laminate stock.
Since you HAVE a .177 R-9, it makes sense to go with the .20. The RX-1 will handle the heavier .20 caliber pellets quite well. I have several .20 airguns including R-9s, R-1s, R-7s, and several Sheridans. The .20 is a good step up in on target energy delivery. I use a R-1 Carbine .20 more than any arigun I have.
For pellets..you'll one need a few .20 pellets to try. The Beeman FTS and Crosman Premier boxed are generally THE .20 pellets for the RX-1/RX-2.