X1ばX2ほどY is more common than X1ばX2だけY and seem to have similar meanings.
I've also seen X1ばX2だけY being used with X2 being used in both the present and past tense, and I don't think I've seen the past tense much with XばXほどY, and occurrences on the web seem to confirm that. For example 「売れれば売れただけ」turns up many hits, but 「売れれば売れたほど」only 4. Same for 「食べる」.
Can someone please clarify the differences in usage and nuance between the two patterns, and the two tenses for X2.
Edit: Since the past tense sounds unnatural to people, here is the transcript of the drama the example is from, in case context helps: