Architecturally, the chips are all the same as they are all dual-core K8 processors.
The QL series chips are the previous generation Turion 64 X2 TL series that now work with the new 780-series chipsets. They clock down to 800 MHz or so at idle and have an 800 MHz HyperTransport link and 2x512 KB L2 cache.
The RM and ZM series are the new generation Turion chips with a much faster (1800 MHz or so) HyperTransport link and a minimum clock speed of between 500 and 600 MHz rather than 800 MHz like the QL series. The RMs have 2x512 KB L2 cache while the ZM series have 2x1 MB L2 cache. Otherwise the RM and ZM chips are identical.
So you will see identical performance out of equally-clocked QL and RM chips as they are architecturally the same and have the same amount of cache. (HyperTransport speed does not affect performance in desktops and laptops.) You will see a little better performance out of the ZM chips as they have more L2 cache. The battery life on the RM and ZM chips will be better than that of the QL series as the RMs and ZMs can run at a lower clock speed at idle and thus draw less power.
I have not seen the SI series- are those Semprons by chance?