Well, actually, you can upsample the readsf~ to choose much faster speeds... however, you do have to wait longer for a deterministic result than you do for a "fast-as"possible" one, such as threading would give you.
right ... but when upsampling the readsf~ it's much more likely to experience a click (disc bandwidth / cpu) than if you do that asynchronous if there is time ... :-)
cheers ... tim