Wow - this question is almost impossible to answer. It really depends on your taste, or what tones you are looking to get. I have paired a number of cabs with my F50, including a homemade 4x12 with 2 V30s and 2 G12T-75s, a 1x12 recto, a 1x12 3/4 cab, and its own internal C90 (it's a combo). They all sound very different. There are others as well, like the Thiele, 1/2 back, plus stuff from other manufacturers.
You ought to bring your head to a store and try a bunch of cabs. Or, do what I did - buy them off craigslist, and then sell or trade them to try others.
If you like the sound of the cab you have, but are concerned about the power, then this may help:
1. Music rarely, if ever, reaches peak power of the amp for any length of time. If you put a 20Hz sine wave into your F50, you can get 50W continuous power out. With a guitar signal, you will probably get 10W at the most, so your speaker can almost certainly handle it. With heavy compression, you can push the actual output power higher, so if you play metal at full volume, you should worry about the power rating.
2. The cabinet has no power rating. The speaker is what limits the power rating - you can try another, like a V30 (60W) or C90 (90W). Or add a second identical cab, so each will take half the amp power.