Luka V4 English sounds nice from what I heard, still accented but not that much compared to her V2.
Most of the English voices require changing some phonemes anyway, the problem with Miku English is that most of her sounds are actually wrongly recorded (tons of L/R issues, volume issues, slurry pronunciation and stuff like that).
As for Gumi's trial, I'd upload it since it's just a trial but my upload speed is pretty much 20kb/s and the file is 1.6GB. :/
Yeah, Luka sounds mostly nice, it's just the odd few words that sound weirder than my Frankensteined versions of them did. Her "saw", if left unattended, is like "sauu". When I did it in the japanese trial I just put "sa", which she pronounced "saah".
But the English voice bank is *definitely* worth it, of course. In retrospect I'd prolly go loopy having to construct every word like I did in the trial.
My first try was pretty rushed, and I hadn't properly tuned my guitar for it, but it managed to sound pretty okay anyway. I'm working on a proper song from the ground up now.
I'd love to try out Gumi's trial, but if it's a hassle to upload that's okay.