So, your end goal is 30mm spacer, 2.5" spring lift, and a body lift?
I am not judging, but I would think this lift/suspension is a bit Frankensteinish to do intentionally. I have seen people end up with stuff like that over a long period of time as their goals change and usually only because they have sunk money into components that didn't end up meeting their needs.
You looking at me?
Seriously though, while a 3.5" spring lift is better than a 2.5" spring lift plus 30mm spacer, there is nothing "Frankensteinish" to a body lift. Body lift accomplishes things that a spring lift cannot, in addition to accomplishing things that it can.
Plus he can likely buy the spacer, run it until he purchases the springs, then sell the spacer and recoup a bunch of the cost on them. Considering they're uber cheap to start with, he won't be out much cost wise.
Another thing to consider is that OME medium springs can be found pretty often used, as that's by far the most common lift people run. Longer springs are less common used. So he can pick up a set of used springs to run until he saves for new longer springs, netting the same amount of lift at a fraction of the price.
That's exactly what I did, and while some of it was due to goals changing over the years it's not really so much "Frankensteinish" as a lift on a budget. Plus it works
really well.
As I understand it, you can run 37" tires on a 4" lift. I have heard some say proper backspacing will prevent rub and others say it's not an issue.
Depends on your setup. 3.5" backspacing will give you less rub than the OEM 4.5" back spacing, so it's a good idea to space the tire out some (different rims or wheel spacer).
Lift and how far you drop your bump stop plays a part as well, you can eliminate all rubbing if you drop your bump stops far enough, but that just wastes up travel.
I have some rubbing in the front, but it's due to the front axle needing to be shifted forward a bit. If I had OEM backspacing, I'd be rubbing rather badly.
Anywho, I think more suspension travel is going to help you and with what you are planning you will end up with a pretty high lift with only 2.5 inches of added coil height, so less travel than the 4 inch lift. Both lifts will require castor correction to set them up properly.
Suspension travel really isn't the issue with either the 2.5" springs and spacer, or 4" springs. See my pics earlier in the thread where I'm maxing out 14" shocks in the rear and 12.5" shocks in the front.
I think you're selling the spring plus spacer lift short. Is it less than perfect? Sure, an all spring lift is ideal. Is it a terrible way to go? Not even close.