The 328JET isn´t this much slower. The cruise speed is lower, yes, but the climb rate is said to be excellent so that they can get on the cruise altitude fast. A thing Fairchild Aerospace features on the 328JET are its very short block times. It is clear that the 328JET can´t be as fast as the ERJ-135 because of the wing design.
To see both jets from the view of a passenger I can only say something to the 328 turboprop. I did a flight on a PSA frame from Raleigh to Pittsburgh and it was one of the most comfortable flights I ever had. On an air show I did a "test seating" on a ERJ-145 and didn´t feel very confortable.
To see both planes from the customer site I think the 328JET seems to lead although it hasn´t sold as many times as the ERJ-135 did, 95 compared to 141. But 120 orders for the ERJ-135 come from 3 big airlines while 19 customers are announced for the 328JET with more to follow soon. Hope you got some bits of information. For some more on the 328/328JET, last year I did a feature on this plane which you can find on my site under the menue "feature".