Try using ISO 800 on the Aptus 75, then process in Raw Develop....WOW, looks beautiful. Raw Develope minimizes the noise much more than LC-10 and especially ACR.
i am using since several months the e75, shooting architecture only.
for my purposes its rarely important how good is the higher iso capacities. more important how good is the nominal iso at lowest setting and here is the e75 doing a great job. i will post soon new full res. samples herre in LL.
i would rate the hi iso with the e75 till iso200 as usuable. please have in mind that the iso in the aptus75 is rated higher than with the e75 this will result in a nominal higher iso from leaf which differ in reality less,-
as far i have seen files from the leaf and from the e75 there is little or no difference in terms of noise between them ( not so surprising for using the same dalsa sensor ). what does leaf in software conversion with nr you also can do later,- with the same or better results.
anyway if i want high iso shooting i use my canons. they are another league in terms of hi iso noise.