Hey Jazzy.
That is exactly what I use, but with different cabinets. Go for the used one. It only weighs 8 pounds more, and it's stable at 2 ohms (1200w), which makes it more versatile, IMHO. If one of your PA or monitor amps goes down at a gig, you can push 2 4 ohm or up to 4 8ohm cabs off one channel. It also makes it possible to mix a 4 ohm and an 8 ohm cabinet on the same channel with no worries.
If you're really after the super-lightweight rig, then maybe it's worth the extra 150 quid, but I had a similar choice to make when I bought mine, and I went for the more powerful used amp.
Regarding clean tone...are you using the Superfilter in the effects loop? I've found that with a bass with a high output, I need to be careful about overdriving the efx loop return. Sometimes this means backing off on the input gain a little. Keep in mind, though, that I just sent my F1-X off to have the transformer replaced (been using it for 11 years), so my observations might apply only to my own gear. it should be back Monday, so we'll see if it still does it.
Hope this helps...