I know there'll quite a few now out there who have done this, i.e. Main applicant gone for ilr and dependant gone for extension in same category.
Now I'm in the same situation, the only problem is, I got my T1 on 6th April 2011 and when I applied extension, I posted my application around 6th of march (as I heard there was quite a delay on processing extensions) and surprisingly enough, I got my visa with all my docs within a week
which in itself wasn't an issue. But when I looked at my visa it was from 12th march 2013 to 12th march 2016 
leaving me almost a month short for my ilr (actually correct me if I'm wrong 28days before my eligibility is 9th march so not really short).The big issue/worry/confusion is, my wife has the same visa expiry i.e. 12th march. Now I'm planning on going for same day application on 10th march. So how will it actually work?
What I've in mind is, go for peo and post wife's application as soon as i come back from peo(as i'll need to send my salary slips with her application)..
In fact, I read that u can apply dependant's extension online, so how does that work?
Can i do it like, complete her online application on the day her visa is expiring and pay her surcharge?
Also, can i start filling application form online before hand and not submit it and when I actually want to submit the application then i pay surcharge that day and then submit the application?
