Simonton 5500 is a good mid grade product. Higher end brands with superior thermal and structural numbers are Okna, Himark, Soft Lite, and Sunrise.

The thermalweld is ok, the ultraweld is a better window though.
I think from a thermal standpoint, the thermalweld beats the simonton.

Tough to compare without knowing the glass package an options but the ThermalWeld is certainly a narrower profile and does have a lower air infiltration rating on average.

I'd say that they are pretty close with a slight edge to the thermal weld. They are not apples to apples however in the sense that the thermal weld is Polaris' mid level offering, while the 5500 is an iteration of simonton's flagship. If you compare equivalent levels, the ultraweld is significantly better IMO.