This would awsome online and off especially on Xbox 360 live, where you could choose to either go solo or play with friends:
Start of by clearing a single room to eventually a whole floor, and get individual and team, times and acuracy scores which would be recorded with a stats page to see who is the world's fastest and most acurate.
Some usefull Info about SAS counter terrorist training (taken from here:
As the men become more proficient, the number of targets in each room will increase. This sharpens reaction times - something that is vital to the success of a real operation. At first there will be just one room, but then the instructors will put three or more in one room. In another the terrorists and hostages will be mixed together. The SAS team will, in a split second, have to identify the terrorists and take them out, though making sure they don't hit any hostages. One favourite trick is to have three or more figures in a room with their backs to the assault team as it enters. Suddenly, all the figures move but only one will be armed. The SAS troopers have no time at all to shoot the armed target. As the course continues complications are added.
Weapons And Ammunition
The Regiment also uses the 'Killing House' to experiment with new types of ammunition. Hostage-rescues invariably take place within confined spaces, such as inside rooms and aircraft cabins. In such areas there is a real danger of hostages being killed by a ricochet. A member of the Regiment describes the kinds of ammunition tried: 'New weapons and ammunition are continually being tested in the "House", and among the latest introductions is a new fragmentation round. It explodes on impact, so if a team has to storm a boat it will hit the bulk-heads and burst without ricocheting, unlike ball rounds.`Also, there's the noise. With all the rounds being fired and the special sound effects it's deafening inside the building.
Be that as it may, the 'Killing House' is essential to getting squadrons up to the required level. But what is that level? An experienced instructor gives his view: 'We are never satisfied with times - one second to draw and fire is too long in SAS reckoning. But it's not just about being able to fire quickly.Guys must be able to identify the bad guys and also prioritise threats. So, when you go into a room you have to clear the doorway - you don't want to get silhouetted - and take the point of dominance so you can sweep the room. You shoot whoever shows intent first. Speed with accuracy that's what it's all about."