Designing a combat=lose campaign, how to give xp?

[gogogome]

My players suggested something weird, and I'm going to give it a try.

Basically they said that they want to be as theoretically optimized as possible barring pun-pun, and because they plan on using wish loops, they want the world to be ridiculously hard. Now I asked for more details and they said they wanted to start at level 1, the average guard is a fully optimized monster at level 10 (Uberchargers), and the only way the PCs are going to survive is by being stealthy, diplomatic, thieving, assassinating, and avoid direct combat until they can get their first wish loop going.

So the setting is gonna start with a peaceful nation fully occupied by an evil invading nation, and as second class citizens, the PCs are going to try to muster up a rebellion/revolution, but they're level 1 PCs with 0 wealth at the start. I was thinking starting the campaign with intelligence gathering encounters, resource gathering encounters, and NPC-related encounters like recruiting, rescuing, etc.

How would I give XP? Giving full XP for stealthily avoiding a bunch of level 10 guards who have 0 detection skill seems overkill and defeat the purpose of the campaign. Anyone have a formula?

For example, a room full of weapons is guarded by 4 level 10 guards. The level 1 PCs create a distraction, sneak past the guards, and liberate the weapons, how much XP is awarded?

[noob]

How hard was it to distract all the guards?
If the guards had good plans like "only send half of the guards away and always keep some near the weapons" and that the guards maxed all perception skills(10 ranks in each) then it might not be trivial to free the weapons.(I wonder do you have weapons who are people too? Else it do not make a lot of sense to say liberate the weapons)
Now the thing for how appropriate is an encounter is seeing which kind of random joe team of level N had a 50/50 chance of succeeding with the base plans(make a diversion and sneak after receiving one or two buffs for that) the encounter cr was the level of that team+4(if the level 1 random joe team have more than 50% chance of sneaking in then it was a lower than 5 cr encounter and it becomes harder to judge since when using skill checks what represents "25% of your daily resources")
now if the guards were just uberchargers and did not made spot or listen optimization they will have around 20 in spot/listen(at level 10) which is lower than the stealth of a specialized level 1 rogue so the cr might be lower than 5 unless the guards starts using help on each other.