What is the Ripple equivalent to https://en.bitcoin.it/wiki/Scalability ?
The limitations on Ripple scalability are substantially the same as the limits of Bitcoin scalability. There are various minor differences, but they don't significantly change the picture.
Ripple already has some scalability features that Bitcoin doesn't have yet, but Bitcoin can easily add them when it needs them. For example:
Ripple nodes don't need to keep history to process transactions.
Ripple nodes can form "clusters" under common administration that divide the cryptographic work.
Ripple nodes can escalate the transaction fees they demand to forward transactions in response to load bursts.
One difference is that Ripple's confirmation time can increase with load. In a sense, Bitcoin's confirmation time can increase with load too as you may need to wait longer to get a transaction in a block. But Ripple's consensus process can take longer if more nodes are participating in it or if a higher transaction level creates more disagreements that must be resolved in the consensus process.
Right now, consensus consistently takes about 2 seconds (which is the minimum). In simulations, the consensus process increases with the log of the number of trusted validators. 100 validators brings it to about 3 seconds. 1,000 validators increases it to about 4 seconds. 10,000 increases it to about 5 seconds.
Consensus time also increases, though by much less, with the transaction rate. Note that consensus time is just one factor in the time it takes to confirm a transaction, though as the network grows it will likely be the dominant factor.