With electric motors and ESC. What would be a good lap time to shoot for?

I've found that I can fly at least .1 to .2 seconds/lap slower than my IC models as the electric setups don't slow down so much through maneuvers.
Lap times are only a guide, it is the time through the maneuvers that is more important.
Vertical eight is a good example; on an IC model it tends to slow a little through the top loop, the electrics power around that top loop with more speed and line tension. Pusher props also give a bit more line tension through that top loop along with all the other high outside loops, eg. overhead eight and cloverleaf.
If you used to fly a given model at 5.3/lap (for example), you could try 5.4 and I think you'll find that you will still have the same performance through the pattern.

I've gone from 5.3/lap to 5.5 with more line tension (on a similar model) and when I converted my Yatsenko Classic to electric, it went from 5.2/lap to 5.4 with the same (or more) performance.