What I Use IA, CA, TA, GA

Hello to all;Well here I go, I'm looking at this "Virtual Airlines" in the net. Well, some of them tells you, ok, you go from airport "A" to airport "B" and you must do it in, lets say 1:25. (one hour and 25 minutes) and ascend to FL230. I have no problems with the calculations of the distance vs. time. You need to perform this calculations in order to pick the aircraft that will fly at "X" speed to accommodate this "airline" time schedule for this particular fly. I figure that from 0 to 10,000 at 250kts and your climb rate, then from 10,000 to FL230 at the climb speed and rate of the "X" aircraft, then your cruising speed after reach FL230, then your descent speed and rate up to 10,000, then below that to land, you add all this times and gives you the time that you will use for this fly, this calculations are needed to pick up the aircraft that you will use for this request from airport "A" to airport "B', because you will not use a CESSNA 172 if, based on this calculations and speeds, you need to go let's say at GS/300kts. Are you bored, well keep reading. The problem, if I know I have to do "Y" speed at my cruise altitude, What instrument I use to know the "Y" speed I need to kept in order to complete my mission. You know that at high altitude the AI in Kts is of no use, because the ram air and,,, well you know. If I use Mac speed I have solved the AI problem, but, aja, What speed I have to convert to Mac (IA,CA,TA OR GA). Question, Does FS2004 use the temperature and pressure in order to affect my parameters, that is if I want to calculate TA then GS (ground speed) using wind effect (direction and speed) or they are only used by the TRFc CONTROLLER to assign departure and landings runways.Please help. THANK YOU ALL.Go easy with my English, Please.