to me quality is not subjective. what is subjective what you think sounds better, some may like the preamp sound of a R4 over a 744. but that's not to say it's better, just like a Neve/SSL preamp, whats better? they are both great at what they are good at, ex. neve has a great colored sound which is great to warm up vocals or a bass track, the SSL is a more sterile preamp that is good with samplers and hip hop vocals....
but a clean quiet preamp is a clean quiet preamp. to me thats what a portable recorder should have, clean high gain presamps. If the pre is clean and quiet, it could be SD, zaxcom, tascam whatever. What the boom op is doing, how you set up your Lav's that is all more important then the quality difference between a 744 and a SXR4
If I were recording vocals and wanted a warmer sound, then I would be interesed in whats better, etc but I honestly think the 744T/SX R4 comparison unecessary as far as quality, they should both be really good and you're only going to hear a difference doing a A/B with the same signal(mic) going into both preamps and then level matched, and even then you'd never be able to tell me which one was the 744T or the SX R4.
I've done lots of A/B tests of high end gear studio gear and in the end the % of differences are at a max of 10-15% you will only hear a screaming difference when you test a 744 preamp against a mackie or a behringer for instance.