Depends on how it was measured and built (custom settings for Perceptual table). But the differences should be much, much smaller than we see between the Seiko vs. X-rite profiles. That's night and day.
Let's say you use an iSis and produce various M-series measurements, then maybe OBA correction and/or post optimization as I do with all my profiles. You could see a difference on a good suite of test reference images (mine, Bill Atkinson, Roman 16). Even when I build custom profiles in i1P using 1700 odd patches, depending on a few factors, I see improved gray balance and saturated color rendering after running a post optimization using my custom target for that task. It can be subtle but it's visible! You're just not going to see that with any 'canned profile' for obvious reasons.
Thanks, Andrew. I was hoping you had a comparison at-hand of Exhibition Fiber, or one of Epson's other "better" papers.
The OP came onboard with the notion that he needed either custom profiles or a RIP in order to get "better print quality." It's been my experience that the canned profiles generally work very well - but then I use Epson's "better" papers almost exclusively (the profiles for which are all, I believe, created by X-Rite; and, again, no intended insult to those who favor Premium Luster). Your example contrasting the custom-versus-canned profiles for Premium Luster - clearly quite dramatic - is, perhaps, somewhat less than representative of Epson's Signature paper lineup? Lending what I'd suggest is false credence to the OP's belief that he's not going to get good prints unless he goes down the road of custom profiles or a RIP.
The reality is that buying an i1Pro 2 or other spectrophotometer is not going to suddenly turn one into a color and profile expert. I agree with Peter that most folks out there today making profiles, either for themselves or for profit, are probably little better - and potentially far worse - in their efforts than are Epson, Canon, HP, Canson, Hahnemuhle, Ilford, etc. My guess is that of those making profiles, very few are at your level (1700 patches!).
Which is not at all to suggest that if the OP wants to learn that somewhat esoteric part of the printmaking business, by all means proceed! But to believe that the canned manufacturer profiles are all rubbish and the only way to get excellent results is to go there, seems patently false.