Hi, hope someone can advise me whether to add a SATA III 120gb SSD to my iMac via USB 3.0 or a SATA II 240 gb SSD. Will there be a real-world speed or performance difference? I know I can try both and test them but would appreciate advice that will save me the hassle. The 120 gb. SSD is a Kingston 400 and the 240 gb one is from OWC. I will add High Sierra to the SSD and boot from it. Thanks.