SLI is promising long-term growth and jobs from the deal, but it was the predicted £50m a year of cost savings by 2017 that helped parent Standard Life's shares jump by 7% to top the market leaderboard yesterday.
On whether any jobs would be retained, chief executive Keith Skeoch said: "We will engage with the talent, we have made our vacancy list available."
The sale offers cash to debt-ridden Phoenix, the former Pearl group which is said by observers to have injected little investment since acquiring the business in 2008 as part of closed life fund specialist Resolution.
Ignis was its fourth corporate identity in the space of nine years, and the business founded on the former FS Assurance in the city will now go the way of one-time neighbours and sector stalwarts Abbey National, Murray Johnstone, and Glasgow Investment Managers.
Mr Skeoch, Standard Life's top earner last year on £4.2m, made clear that the merged business would be looking to retain particular "talent" rather than the base in Glasgow, or in London where Ignis employs a further 140.
"There are some synergies, which will mean some job losses, but we are a very strongly growing organisation - we have created 400 jobs over the last five years," Mr Skeoch said.
"We will continue to expand. I have got just south of 100 vacancies out in the marketplace and we will probably go up to 200 vacancies in total over the next two years.
"We are hopeful that there will be some pockets of high-performing talent and we will get some fills for these vacancies from Ignis."
The 400 Ignis staff are split roughly equally between fund management, operations and support.
While SLI has a floor in the "Gherkin" landmark building in the City of London, it employs most of its 1164 staff in Edinburgh.
SLI's first acquisition after 15 years of organic growth will add £59 billion to its £184bn of funds under management and take its proportion of non-Standard Life assets to 64%.
The securing of Phoenix's four insurance funds, among them Scottish Mutual, Scottish Provident and Alba Life, in a "long-term strategic alliance", is part of the deal.
Mr Skeoch said it would add £44bn to the £85bn of money already run for its own insurance parent, creating a platform for SLI to win the management of other insurance funds, including those acquired in future by Phoenix.
"It means we will be running money for five life insurance books and 10 other insurance companies. This will make it quite clear to the market that we are open for business to be part of an increasing trend of outsourcing assets."
SLI cites a report out this month which estimates $1000 billion of life insurance assets are set to be outsourced in the near future, which is less than 8% of the total assets across Europe, the US and Asia.
Mr Skeoch said: "There are real signs of strategic opportunity with this deal as well as financial benefits that come through in the short run."
He said the group had "quite high hurdles in terms of acquisition criteria".
Pitched at 7.5 times Ignis's £52m profit last year, the deal would enhance earnings in 2015 and enable SLI to target a 45% earnings margin by 2017 from its current 37% and the 35% at Ignis.
The one-off costs are estimated to come in at £75m.
Mr Skeoch added that some successful investment houses had been ruled out as targets in the past, because it would have meant "banging two cultures together".
Ignis was "one of the few deals we could do", and SLI was "one of the few houses in the UK that could take £44bn of assets and just plug it in", the chief executive said.
But he went on: "I think there will be synergies there, but actually it needs administration and servicing, we need some of those people as well, particularly if we are going to win more of these assets." Ignis achieved £1.9bn of net inflows in 2013, which SLI showed would have created a total £12bn for a merged group, well ahead of principal rivals M& G, Schroders and Legal & General.
The Ignis momentum was largely down to the success in fixed income with its Absolute Return Government Bond, run by the well-regarded "liquidity team" based in Glasgow, also home to the sector's flagship £920m UK Commercial Property Trust.
SLI cites government bonds, liability management, emerging market debt, credit and real estate as Ignis's strengths, alongside strong performance with 85% of assets above benchmarks.
Mr Skeoch said SLI's strategy had always been that any acquisition must "deepen our investment capability and broaden our client reach".
The deal includes an adjustment mechanism to compensate SLI for asset loss, but Ignis's life book is said to be running off at a normal rate and the £59bn total to exclude loaned-out assets which Ignis had previously counted.
Standard Life shares closed up 26.2p at 400p while Phoenix rose 31.5p, or more than 4%, to 741.5p.