Selecting different cruise profiles doesn’t seem to have any impact on fuel consumption calculated by simbrief. Judging by what can you see in POH for BE58 there should be 11-23% difference in fuel consumption when comparing 24.5/2500 and 20.5/2100 profiles depending on altitude.
Here are my calculations:
6000ft
20.5/2100: 10.6 GPH / 167 kts = 6.347 gal/100nm
24.5/2500: 15.6 GPH / 200 kts = 7.800 gal/100nm
Diff = +22.89%
10000ft
20.5/2100: 10.7 GPH / 174 kts = 6.149 gal/100nm
24.5/2500: 13.6 GPH / 195 kts = 6.974 gal/100nm
Diff = +13,42%
14000ft
20.5/2100: 9.4 GPH / 167 kts = 5.629 gal/100nm
24.5/2500: 11.8 GPH / 189 kts = 6.243 gal/100nm
Diff = +10,91%