Hi Gill
I sail solo against F18's and A Class. We are all approximately the same standard. I'm 175cm tall and weigh 77kgs. We can practically predict who will win a race before it has started based on the wind strength alone. Lightwinds 'A' medium F16 strong F18. If you go two up then the stronger the wind the more likely you are to beat the F18. However, alot will depend on which scoring system you use. At our Club we have just changed from SCHRS to Texel (both formula based) whilst in America they can use USPN (based on elapsed times). This makes a considerable difference to their ratings:

type texel uspn
F16 1.00 1.07
A Class 1.01 1.03
F18 1.01 0.99

As you can see now would be a good time to pack your bags, move to the USA and kick some F18 butt. Or do the American F16 sailors eat to many Mc Donalds to increase their rating.
On a more serious note, yes you can beat F18 sailors of a similar standard whether solo or two up but you will find it more often than not happen during a certain wind range.
You will not be disapionted with a F16 they are a much more enjoyable boat to take around a course compared to those overweight F18's
Go For It.