Plumbing sizes and drainage

[gregzz4]

I'm considering, for multiple reasons, a sump rebuild
Before I do so, and build a shorter height/longer one, I've a drainage issue to solve ...

The reason for this thread is I can't run my Eheim 1262 full out as it overcomes the main drain

I currently have a 1" drain and am using 1" PVC
The bottom of my DT bulkhead (1-1/2" below the glass) is only 5-6" above the level of my sump

A lot of you with under-tank sumps probably have a drop of 12-14" whereas mine is less than 8", and runs quite a ways (6' of lazily sloping horizontal runs and through 4 90s)

Would it be worth my while, with a 1" bulkhead, to step up the drain pipe to 1-1/2" or even 2" and see if there is an improvement in drainage capacity ?
Or is there a disadvantage to larger drainage that I'm not aware of ?

Something else to think about is the angle of the slope as I recall something about there being an ideal magical # that the Romans figured out and is one reason I'm considering a shorter sump - 16 tall instead of 19

Any help is much appreciated