The Screwy31 is a USbattery, and it required(s) rather absurd absorption voltages and EQ charges every 14 to 18 cycles for me to get those 500 cycles from it. It is actually up in the high 500 cycle range now, but the cycles are lighter and less frequent, but might still be ~50% of its remaining capacity.
To be a valid comparison i would need to have cycled the life of a trojan group31.
And GC-2s are a much different animal than a group 31 as well.
Faced with the choice the OP has, I'd go for the trojans, but honestly the US Battery did pretty well, as long is it got those extended top charges and frequent equalizations. Getting that SG upto 1.275+ just took a lot of time, when cycled to 65% or below.