Lets assume 3 players start playing DUST 514 at the same time. We'll call them "Noob 1" to "Noob 3"

Noob 1 has several hours to play DUST every day. (hardcore)
Noob 2 has a solid session of 10 hours on Saturday, and a couple of hours on Sunday, but can't play the rest of the week. (regular)
Noob 3 only has a couple of hours to spare every week. (casual)

Now lets look what happens using option 2 from the poll:

Noob 1 (hardcore) hits the rolling daily cap, every day. Part of his playtime is spent with SP limits every day.
Noob 2 (regular) doesn't play every day, so the SP cap rolls over during the week, allowing them to approach - but maybe not hit - the cap every weekend. He'll probably earn a little bit less SP than the hardcore Noob 1, but not by much.
Noob 3 (casual) doesn't push his limits, and is a casual player, so he's always going to be falling behind anyway.

Lets see what happens with option 5:

Noob 1 (hardcore) races ahead, leaving everyone else in the dust (see what I did there? Terrible pun is terrible)
Noob 2 (regular) will fall behind during the week, and when he does get to play, will only lessen the gap a little bit, rather than actually feeling like he has any chance. After a couple of months, Noob 1 will outstrip him horribly.
Noob 3 (casual) is still a casual player, and not being held back too badly.

Now, lets compare two hardcore players who start playing the game 6 months apart. We'll call them "Experienced Player and Noob.

Using option 2:

Experienced Player hits the daily cap every day, and if he has a day or two off, the rolling cap gives him the previous day's cap on top of his current day.
Noob can play a similar amount, and get similar SP earnings, allowing him to keep pace with Experienced Player's SP earnings. As with Experienced Player, if Noob misses a day or two, those days' SP caps roll over to allow him to maintain his position with a longer-than-usual session if he wants to push for it.

Using Option 5:

Experienced Player gets to race forward unrestricted on SP. Missing a day means missing out on a day's worth of SP.
Noob has exactly the same advantages and restrictions. If he keeps up, his SP earning will allow him to keep pace with Experienced Player, still a LONG way behind, but not falling further behind. If he misses a day, however, that day's lost SP earnings will mean he falls further behind.

My vote for option 2 stands.