another question is do you need Ø1.5 drain lines?
A Ø1.5 Drain line running at full siphon will do in the neighborhood of 3700 GPH, compared to a Ø1.0 that will do about 1600 GPH
You know what return pump you will use so you need to decide
I use both 1" and 1 1/2" drain lines on my tank (three 1" siphons, though none of them at anywhere close to full capacity; then 1 1/2" for the two backups) ..... but it's 450 gallons. On more reasonably sized systems just 1" may suffice.