The quality of Ricohjpnr01 DVD+Rs varies extremely. Even discs of the same batch perform differently. One example: I use Tevion DVD+Rs with Ricohjpnr01 media code. I get them in a local supermarket in small quantities for a decent price. My first disc of the batch was a coaster: Unrecoverable read error at the beginning of the 8x zone :Z .
To my surprise, the second disc of the batch could be read perfectly @16x max. The graph in CD Speed is completely linear - no single slowdown! I burned further discs of the same type @8x and all of them could be read perfectly.
But the one coaster shows, that the quality varies in some cases and might even result in a coaster. So I recommend to burn these media @6x. AFAIK, the speed limit in the official NEC firmware is 6x - absolutely right in my opinion.