Well yes those are rather down-market eyepieces for a fast dob.
Unless you want to pay rather high prices for fairly esoteric eyepieces, one of the best budget sets around are the Edmund RKE's, they are designed specifically to match f/4 Newtonians, and have a 50 degree field of view in focal lengths from 8 to 28mm.
http://www.edmundoptics.com/onlineca...productid=2075
Having had a full set until recently, you will have to pay several times the price of these to find a better eyepiece.
If you want to economise, buy the 28, 15 and 8mm and use your barlow.