i5 3.8 vs i7 4.2

hello all,

glad part of forum. have 2014 mbp13 , upgrade imac (not pro) within next month or so.
not gamer, big demand throw @ imac lightroom , photoshop editing 24mb+ raw image files. not shooting many videos, want keep future options open newest dslr has 4k video ability. editing videos seems next logical step me, can't see being primary use imac. first love photography, not videography.

have eye on amd 580 w/8gb, 512ssd , 8gb ram. won't have problems upgrading ram, , end 40gb total on board after getting imac in.

questions:
1) lightroom , photoshop take advantage of i7 enough justify upcharge it? ie., disappointed in i5 3.8 in long run?

2) heat. i've heard i7 can hot, i've heard i5 isn't far behind in heat generation arena. lr , ps tax i5 (or i7 matter) point hot?
realize can stop processor using turbo mode, , assume help, concerned; heat = fan noise. mbp silent.
3) regret 1 processor on other due fan noise?

i've worded in way makes sense, , i've asked appropriate questions.

in advance comments , thoughts!

 

i have same dilemma. i7 on i5 open i5 year (if upgrade)

 

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