For the paper I'd wan't to mimic the thousands of bench rest shooters across the country that use 36x & up. Weaver is a good one for the cost, Leupolds are still popular, & the high dollar March will be seen more than you think.
The steel out to 500 would require some repeatable & dependable target knobs & a 6-24 would be poplar.
I don't quite understand why you'd think the Sig would would be silly excess unless it's the silly excess of gadgetry.
They may work out fine, but have yet to be proven in the real world for the long run.
If you already have a Sig, what do you have to loose by trying it ??