The V6 engine delivers 154kW and 252Nm of torque, giving the GS 250 a claimed 0-100km/h time of 8.6 seconds - a mere hair short of the IS.
Matched with an electronically-controlled six-speed automatic transmission, the V6 offers fuel consumption figures of 8.9 l/100km.
The four-cylinder 520i delivers 135kW and 270Nm, with a 0-100km/h time of 8.0 seconds and fuel consumption at 6.4 l/100km.
The more powerful 528i four-cylinder lists 180kW and 350Nm, with a 6.3 second 0-100km/h run and 6.7 l/100km. How realistic those fuel figures are remains to be seen, however.
These lower-end variants in the 5 Series range are strong sellers for BMW in Australia - a market demand that Lexus will be looking to capitalise on.
As with the rest of the GS range, the GS 250 will be available with the Lexus F Sport kit, adding styling and handling tweaks.
The new GS range will hit Australian showrooms in the second quarter of this year, with pricing to be revealed closer to launch.