My buddy once told me:
"buy once, cry once"
I went ahead and got kings after 3 years of ownership. My perspective is - if you're going to upgrade anyway, how much more would it be to get what you'd prefer vs what you're trying to spend? I started off with TRD Pro suspension, then upgraded my coils which gave me a lift. Now I have the kings as they're rebuildable but also height adjustable up front.
Keeping your goals in mind should probably the top motivation for your upgrade. Are you daily driving this and upgrading for comfort? Is this for a weekend warrior?
I'm not sure what springs are compatible with the 5100's but 6112's are 2.5" shocks so most suspension manufacturers can provide the spring rates you're looking for (e.g. King, Icon, Eibach). Something to keep in mind is the money you're going to spend in total - upfront costs and backend (servicing/replacing).
Perhaps I just confused you even more but at least you'll have more info to work with