How should I spend my money?

[K-amps]

I am happy with the 28-135 on my crop body. Just assumed it would disappoint on FF.

Just try it against a $100 50mm 1.8 mk.ii and see what we mean...

It is great for $250 used... but it has it's limitations, these will be exposed by the FF. However keep it till you have the FF and then decide for yourself.