Flooring / Subfloor

[Sean Pincus]

I am renovating a house in Philadelphia. I have old growth pine tongue and groove 'subfloor' on top of the flooring joists (3/4" thick). I then have a 1/4" thick layer of what appears to be MDF or possible masonite. I want to add another layer of subfloor to strengthen the floor after patching in certain areas. Note: I put new beams in the basement to support the floor joists at the midpoints (it's an old house).

I have access to a lot of OSB sheathing 7/16" for free and was wondering if that will hold up well if I put hardwood flooring on top of it. Typically, I wouldn't put OSB down but given that the T&G pine is underneath it all I don't see it as an issue. 

Can anyone advise whether I will see issues with using the OSB?

Thanks,

Sean