Hi. I have recently moved to leytonstone having previously lived in stratford. I can't help much but will at least bump up your thread! 9 years ago we looked at forest gate, but were put off by commute as when we tried it out on a Saturday afternoon we couldn't get on a train to Liverpool Street. There are however plenty of buses down romford road to stratford. The more desirable part of forest gate is close to wanstead flats, I suspect not where you are suggesting, and probably as competitive as leytonstone.
We have always enjoyed a vegetarian south Indian meal on green street, though not sure if I would want to live there. Currently the parking is terrible in that area, and traffic can be gridlocked on match days. I presume the latter at least will improve when west ham relocate. The area has, IMO, a vibe of non-affluence.
In general I would say there is more housing available for a better price for a reason. Our estate agent tried to push us to houses off portway, towards plaistow. There are a number being refurbished there. The area is very mixed in housing stock, I get the impression a lot of bomb damage resulting in estates/flats I.e. not so pretty IMO. There are still plenty of Victorian terraces (although some developers are gutting and losing all features, but I also have the impression many houses may need gutting). I have been told west ham park area is attracting families. However the only family I know round Upton park intend to move out in a couple of years to somewhere they consider more family friendly.
Oh, I wouldn't recommend Newham hospital for babies.
Good luck, and don't be afraid to put in asking price or less offers in leytonstone especially if it is that or walk away. Having studied sold prices, and watched sold stc come back on the market I am not convinced it is quite what the estate agents say. Some houses even get reduced!