As an Xpress and Adrenaline owner – I would advise you to hang on to your Xpress unless you have a compelling reason to upgrade.
Adrenaline so far has had major bugs – which gets better with each release and then also goes backwards because new bugs are created. In short, it’s not a perfect beast. As for FCP, I can’t say except that the cost of investment should be lower. FCP is a relatively lower risk and cost so take it for a test run.
I had the same thoughts as you in terms of replacing an aging suite – I’m running Xpress Elite 6.0 – it’s not as fast in rendering compared to Adrenaline but who cares, it’s a workhorse. We still can’t render sequences longer than 7 mins in Adrenaline without it choking. In theory it’s a beautiful machine, but the bugs are lurking there. Meredian may be at the end of its life span but it’s still more stable.