LTSpice IV simulation speed adjustments

[ElectroPhysics]

Hi everybody. how r u.
i'm using linear technology's LTSpice IV to simulate my dc/dc switching power supplies. for that I'm using the chips from the same company. the problem is that when i simulate the circuit using LTSpice IV the simulation speed that it shows is only 25microsecond/s which is too slow and i have to wait for a lot of time for the simulation to end. when i searched examples given in this software such as "astable" the simulation speed there is 145milisecond/s which is very good. i have tried my best to solve this issue i.e. by searching every menu given in the software but could not find "simulation speed" button/form. please tell me how to adjust the simulation speed for my circuits.

 

[ElectroPhysics]

another thing that i noted in "astable" example that if i change the circuit slightly i.e. for example connecting a 200uF capacitor to the monitored output, the simulation speed shoots from 145miliseconds/s to hundreds of second/s as when the curve become flat. Does it conclude that simulation speed in "transient analysis" is curve dependent and can not be adjusted by will?