The only way to know about how much you will yield is, previously grown strain, similar medium, same pot size, same lighting source and same nutes. For me the largest indicator is the size of the pot (soil). If your growing in anything under 3gal it would be hard(not impossible) to get an oz with most strains.
What size pots are you using for flowering? And yes get the hps if you could
. Larger one would be better, still the 75w would be way better than the cfls. If you start getting serious about growing invest in a 400w+ hps.