Spring platform is lower on SF than SG , they direct bolt on, SF can be bolted to SG & SG can be bolted to SF .
Due to Spring platform difference you ideally need custom springs to set a desired ride height and as you want lower & increase spring rate mildly it no extra expense .
Springs to be used with SF ultra sr would need be longer than specific SG excel-g's due to differing spring seat position on strut .
Unfortunately easy options are limited on struts, you got sf ultra sr, sg excel-g, sachs (bit firmer than excel G) or pedders kits .
You can custom fit Bilstein inserts but not cheap for decent effort.
Excel G's are superb for the cost, no hassle fit & easiest to specify custom springs over phone.
sti or wrx wagon struts can work out cheap upgrade if find decent used set but ideally want custom springs especially rear to get sit right .
Most people really like the excel-g's, i've used them on XT with custom springs lowered 30mm & owner been very happy with setup,
throw in group n rear mounts-pillow balls mod to front mounts, rear stabilizer mod, strut brace & lower brace & make sure bushings good or replaced, allignment setup & it should feel far more stable/precise at speed but remain compliant for devon road daily use so won't fatigue you from harshness .
wrx or sti struts are worth considering especially if aiming lower 50mm+ . Done one with inverted struts modded with greasing nipples, standard wagon springs lowered 65-80mm & rear was too low to front so we got springs made up off of the wagon springs .
Choices are up to you & your budget and your use, if carrying load or sometimes towing you need build this into your final package spec .