Lattice matched InAlN/GaN heterostructures potentially offer a high reliability alternative to AlGaN/GaN devices whilst theoretically maintaining the high power/frequency performance characteristics. This study uses commercial device simulator and equivalent circuit models to directly compare the suitability of In0.18Al0.82N and Al0.3Ga0.7N as a barrier layer in conventional GaN-HEMT structures with a focus on the DC and RF current response over a range of ambient temperatures with respect to the parasitic impedances commonly reported to inhibit InAlN fulfilling its theoretical potential.