Replying to FD Lens

Yo, NS I come to you in desperation.

So I have my T2i with the shitty 18-135IS and my nice old nikon 50mm f/1.8 with an adapter obviously.

Now, I've listed my 18-135IS on craigslist, where I assume someone eventually will buy it and then I plan on getting the Tokina 12-24.

However, in the meantime, I want to buy a nice SHARP fast zoom lens. My 18-135IS is literally the least sharp most garbage lens ever which isn't a surprise because its variable aperture.

I've been on DVX user and came across a 35-105 f/3.5 FD mount lens. I've been wondering in general, when using an adapter (a quality one) to adapt FD to EF, is the quality of my photos going to depreciate? Are FD lens really worth the hassle?

Thanks