Not much help this, but in the past I have done some load testing on OACS 4 (earlier in its develpoment life) cos I had the same query.
It would appear (and I am not a PG expert) that given then unqiue keys in that table, the fact that most references to the table are against direct key values, and that the majority of accesses to that table appear to be inserts, I don't think its too much of an issue. Certainly Oracle doens't seem to experience significant degredation from high numbers.
I'm sure someone else here can be more definitive and will be better informed about PG.
