Belltech Shock replacements

[LoSRx7]

2011 Yukon lowered on a Belltech 2/4 drop done ages ago. Replacing a bushing on the front upper arms soon, and while i was under the vehicle, i noticed the rear shock cases were bit rusty. New England weather sucks sometimes, should I be concerned about this?

If I wanted to replace these 25003 fronts and 2410FF rears all together, are there any recommended upgrades (smoother) to these?

Thanks,
-LoS