In Hawaii? I wouldn't honestly worry about it.
Your highway drives are not long and the speeds in town are well within what a 2.5L can do easily.
If you leave Hawaii and want to move some place with more hills and longer distances on the highway, then I could see a 4.0 in your future.
I have a 2.5L. While I wouldn't mind a 4.0L, the 2.5L has worked well for me and handled my wheeling offroad and DD duties just fine. Just plan what you want it to be and work backwards to see if the 2.5L base will meet your needs.
I knew I wouldn't go over 33's or a huge lift - my wife is 5'1" and I'm not into the real hardcore stuff - I have to drive it home. For that, the 2.5 works.
I regeared, strengthened where I could given my budget and enjoyed every drive I've had in it.
The 2.5 can be a great starting platform for casual to moderate wheelers. Now if you plan to get into deep mud or rock crawling and plan to pound on it offroad, then go with the 4.0. The transmissions are stronger, the D44 is an option for a stronger axle, and you generally have a higher starting point than the 2.5 durability-wise.
I have tackled mud and rocks with mine as part of my wheeling, but I don't seek out the insane stuff and risk breakage.
To mine, I've done:
JKS BL, MML, disconnects, control arms, track bars
regear to 4.88 for the 33's
upgraded D35 shafts to Yukon 30 spline
Since doing all that, I have not had any mechanical failures or damages due to offroading other than a flop. But the 4.0 sheet metal is the same as the 2.5.