Chatty, I would take the higher at $890 or look at the differential between $890 or $1200 with about 4.5 years remaining, thus there are 2 scenarios (if I interpreted your question above, this is!) (I've averaged to age 85):

1. Option 1 where you continue widows benefit and then switch to your personal benefit at age 70:

$750 for 4.5 years = $40,500 (widows benefits) + $1,200 for age 70 (once you switch to your benefits) = $216,000. Overall total = $256,500 (estimate w/out inflation).

2. Option 2 where you switch to your benefits now: $890 x 234 (mths) = $208,260 (estimate w/ out inflation).