I wouldn't expect a huge leap in performance considering it's a beta. I would look for videos of iPhone 4S and iPod Touch performance videos on YouTube. I believe the 4S share just about the same specs with the 5th gen iPod Touch.
I also had the 7.0.4 jailbreak on my iPod back in February, and I had a lot of lag and slowness too. But I ran the iOS 8 betas on my iPod touch ever since the first one on June 2nd. Beta 1 ran almost the same as 7.1.1. I am now on Beta 4 and it runs smooth, but some folder lag. But iOS 8 will run good on the iPod when iOS 8 will be released in September.