Wait, since when do cyberlimbs not affect movement rate? Limits I'm aware of as per Aaron's reading in the FAQ thread, but movement rate? Why wouldn't cyberlegs influence movement rate, for example, when gear such as hydraulic jacks specifically aid in running tests?
Specifically, movement rate is listed as being "determined by metatype" on page 161, referring to the movement rate table on page 162. This table lists AGI x 2 and AGI x 4, making no mention of inherent attributes as the basis for the calculation. As per the Cyberlimbs chapter starting on page 455, you "take the average value of all limbs involved in the task", and I believe this to be critical since it's a task, not specifically a test.
So the STR/AGI 4 Elf with a single cyberlimb of AGI 9 would use his average AGI (depending on what limbs the GM deems to be involved in the task of running) of either 6 ((4+4+4+9) / 4 = 5.25 rounded up) or 5 ( (4+4+4+9+4) / 5 = 5, or (4+4+4+9+4+4) / 6 = 4.83 rounded up). for the calculation of movement rate.