iMac 27" Mid 2010 & SanDisk Extreme PRO SSD

I am also interested in replacing my internal 1TB /7200rpm (SMART status Failing) on a iMac 27 Mid 2010, checked the SATA controller it is a intel series 5 chipset 3 Gigabit, AHCI version 1.3 supported.

I am happy with a 240/250 GB SSD but unsure which model would suit best. Because of the SATA II limitation what benefit would i see with a higher end EXtreme Pro SSD over a cheaper model?

Because the SATA is II can you just half the SATA III performance spec for a SSD interfaced to a SATA II controller ? Will it not run at the 3 GB limit ?

Without the sandisk software tools for Mac how can i update the SSD’s firmware using a bootable USB stick, my CD/DVD drive has stopped functioning ?

I am interested in sandisk because of TRIM support on both the SSD and OSX 10.10.4.

My aging iMac has 12GB RAM, i would like the sweet spot on price/ performance on the disk subsystem.

 Sorry for double post (email me on reply issue) got me too!!