ILR Eligibility - Tier2/1 combination

Apologies if this kind of question is answered elsewhere, please direct.

I have been on a combination of a Tier 2 visa & Tier 1 visa continuously for a period nearly to 4 years now.

Here are the details on my visa details for your reference.

Tier 2 Visa - Granted on 28/04/2010 valid until 28/05/2011 (1 year and overstayed for 16 days to get the visa renewed)
Tier 1 Visa - Granted on 13/06/2011 valid until 13/06/2013 (2 years)
Tier 1 Visa 1st Extn - Granted on 17/04/2013 valid until 17/04/2016 (3 years with a overlap of 57 days)

I came to UK on 18th July 2010, approximately 81 days late from the first visa grant date.

I've two questions,

1. Am'I eligible to apply for ILR using the Tier2/1 combination?, If so, what is the best time to apply for the same, May 2015 or July 2015?

2. If not, the only choice is to use the Tier 1 stay alone for ILR purpose, then I'll be short by 57 days on 17/04/2016 and I'm hearing that T1 G ext will no longer be available after April 2015 - what do you reckon the best approach would be for me?

Any guidance in this regards will be highly appreciated.

Thanks in anticipation.
Ginu.